---
title: "What You Need Before You Start"
series: "Build Something You Actually Need"
position: 2 of 8
author: "Buddy Lien"
language: en
edition: source
html: https://legion.tw/en/build-something/what-you-need-before-you-start
markdown: https://legion.tw/en/build-something/what-you-need-before-you-start.md
---

# What You Need Before You Start

Your first app can be a proper Windows application that you open from a shortcut and use to do your work. You do not have to graduate through a succession of fake dashboards before you are allowed to have a Save button that saves.

In the first version of this series, I chose a browser-based starter project because you hadn't written code before. Frank pointed out that his wife's first project with Codex was a powerful native app for making glitch art. She learned by directing something she wanted to use; the implementation was the AI's work. I had confused your experience with its capabilities.

For our Visit Book example, we'll use Codex to build with Tauri. Tauri is a toolkit for making desktop applications. Codex knows how to work with it; you need the name so you can request it. We'll ask for a Windows installer and records saved on your computer. You won't need to keep a website running to use your own appointment book. [Tauri's installer documentation](https://v2.tauri.app/distribute/windows-installer/) describes the Windows packages the builder can produce.

A browser app is useful when people need to reach the same service from different devices. Lovable, which builds and hosts this website with us, is a good route for that. Here, you have a Windows computer and want an application on it.

## Open the project in VS Code

Install [Visual Studio Code](https://code.visualstudio.com/docs/setup/windows), usually called VS Code. Choose the Windows User setup and run the installer. VS Code lets you see the files in a project, open your notes, and run a terminal in the same window. You can read a file yourself or ask Codex to explain it.

In File Explorer, open Documents and create `My Software`, then a folder called `VisitBook` inside it. In VS Code, choose **File → Open Folder** and select VisitBook. If it asks whether you trust this folder, this is the empty project folder you just created yourself. The file list on the left will fill up as Codex builds. Clicking a file opens it in the main area. For now, there is nothing to read.

Choose **Terminal → New Terminal**. A panel opens at the bottom of the window. That's the terminal: a place to type commands and read their replies. On Windows, use the PowerShell profile; the dropdown beside the terminal's plus button lets you choose it. Microsoft's [terminal guide](https://code.visualstudio.com/docs/terminal/basics) shows the controls. The terminal normally starts in the folder you opened. You can type `Get-Location` and press Enter to see its full address.

The open project folder is your workspace. You can learn the other controls in VS Code when you have a reason to use them.

## Two ways to open Codex

You need a Windows computer, an internet connection while Codex works, and an account with access to Codex. You can use the [Codex desktop app](https://chatgpt.com/codex/app), with its project sidebar and conversations, or the **CLI**, which runs in a terminal. CLI means command-line interface: you launch it by typing a command. Frank uses this version. I recommend trying it, even if you have never used a terminal. Once Codex opens, you talk to it in ordinary language.

If you prefer the desktop app, install it from the official page, sign in, and open the VisitBook folder you just created. Some OpenAI desktop releases present Codex through a selector inside ChatGPT; choose Codex if that's the interface you have. You do not need both interfaces. The [desktop quickstart](https://learn.chatgpt.com/docs/quickstart) shows the current folder-selection flow.

For the CLI, use the PowerShell terminal you just opened in VS Code. You'll see a line ending in `>` with a cursor waiting for you. That's where commands go. Copy this official Windows installation command, paste it there, and press Enter:

```powershell
powershell -ExecutionPolicy ByPass -c "irm https://chatgpt.com/codex/install.ps1 | iex"
```

That line downloads and runs OpenAI's Codex installer. The temporary `ByPass` setting applies to the PowerShell process running that installation; it is not an instruction to permanently disable your computer's protections. This is the command published in [OpenAI's Codex repository](https://github.com/openai/codex/blob/main/README.md). Use the official address as written. If you already have Codex installed, skip the installation.

Close VS Code when installation finishes, reopen the VisitBook folder, and open a new terminal, so it picks up the newly installed command. Type `codex --version` and press Enter. It should print a version number. If Windows says it cannot find `codex`, copy that exact message into the AI chat you already use and ask for help completing the installation.

If the terminal is already in VisitBook, you can start Codex there. If you opened PowerShell separately from the Windows Start menu, or need to change folders, use `cd`. Copy VisitBook's full address from File Explorer's address bar. Type `cd `, then paste that address inside double quotation marks. For example:

```powershell
cd "C:\Users\Alex\Documents\My Software\VisitBook"
```

Use your own copied address, not Alex's. `cd` means change directory: tell the terminal which folder you want to work in. The quotation marks keep the spaces in the name together. Then type:

```text
codex
```

Follow the sign-in instructions and choose your ChatGPT account. Codex should now be working in VisitBook. You can ask, “Which folder are we working in?” and compare the answer with the folder you opened in VS Code. In the Codex desktop app, selecting that same folder does the same job. You can keep VS Code open beside it to read the project files.

An ordinary chat can give you code to copy. Codex can work on files and run the tools that turn them into an application. If it hands you pages of construction instructions, ask it to do that work in the project folder and explain only the actions it actually needs from you.

Put any notes from article one in this folder, or ask Codex to save your description here. That way you can return next week and find what you wanted to make without remembering which part of a long conversation explained it.

## Ask for the application you want

Here is a starting request you can copy. The businesses will be fictional while we learn.

> Build a Windows desktop app called Visit Book using Tauri, in this project folder. I have never written code. Please handle the programming, install the build tools you need from their official sources, and explain any step that needs me to do something on my computer.
>
> I call businesses to arrange visits. I need to find a business, record what happened on a call, set a reminder to call again, and record an agreed visit time. A callback is different from a visit. Let me change or cancel an appointment without losing the earlier notes. Show the agreed visits for a day using those same saved records, so changing the appointment changes the day's schedule too.
>
> Start with invented businesses. For now I am the only person editing on this computer. The app should save its records locally, work without internet once installed, and preserve the records when I close it or install an updated version. Give it a clear, attractive interface that is comfortable to use while making calls. I want to be able to correct mistaken entries.
>
> Read this back to me in terms of what I will do in the app. Ask about any decision that changes how the job works. Handle the technical choices yourself. After we settle those questions, build it, check it, and give me an installer and a normal way to launch it. Save the agreed description and instructions for returning to the project in the folder.

Read Codex's response. If it asks whether a changed appointment should notify somebody automatically, answer for this practice project: no, you will contact people yourself. If it asks you to choose between unfamiliar database technologies, ask it to recommend and implement the one that fits the job. You can require a clear explanation without taking over the engineer's work.

When the description is right, tell it to build. It may need to download tools before it can produce the app. Tauri's Windows setup includes Microsoft's build tools and Rust; these are things Codex uses to make the program. Having them installed does not enroll you in a Rust course. The [official prerequisites](https://v2.tauri.app/start/prerequisites/) give Codex a reference if it needs one. An installer may ask for your approval or require a restart. Have Codex explain the requested action, and resume in the same project afterward. If installation fails, ask Codex to resolve the failure and continue building.

## The first time you use it

Ask Codex to open the installer it just produced and guide you through installing Visit Book. If Windows displays a warning about the publisher, show Codex the exact warning and have it explain how it relates to your own newly built installer. You don't need to disable Windows protection generally to install an app you've just made.

Now open Visit Book from its normal shortcut. You should be looking at the appointment tool, not the conversation in which you commissioned it. Pick an invented business, record that you called, and enter a callback for tomorrow afternoon. Check the visit schedule. That callback should not have become a visit. Then agree an appointment, move it to another day, and look at the schedule again. Can you understand what happened? Can you still find the note from the earlier call?

Close Visit Book and open it again. Your records should be there. If they aren't, tell Codex exactly what you entered and what disappeared. A claim that the build succeeded does not answer that complaint. You asked for an appointment book, and appointment books are supposed to remember appointments.

You now have three related things on the computer:

| What | How you use it |
| --- | --- |
| The VisitBook project folder | Open this in VS Code to see the files, and work with Codex here when you want to change the software. |
| The installed Visit Book app | Open this when you want to record calls or use the schedule. |
| The app's saved records | These contain your notes and appointments. Ask Codex to show you where they are stored and how to back them up. |

Updating how the app looks should not replace the appointments you entered. Later, GitHub will help preserve the project files, and we will arrange a separate way to recover the records.

Before you leave, ask Codex to put a short `START-HERE.md` file in the project folder explaining how to open the app, where it keeps your records, and how to return to building. The `.md` ending means a plain-text document; Codex can open and explain it whenever you need. Then change one thing that bothers you. Make the notes easier to read, move an awkward button, or ask for a better way to see tomorrow's callbacks. Install the revised app and make sure your previous entries remain.

To leave the CLI, wait for the current work to finish, then press Ctrl+C; follow its on-screen prompt if it asks you to press again. To return, open the VisitBook folder in VS Code, open its terminal, and run `codex resume`. Choose the conversation for this project. In the Codex desktop app, reopen the project and its conversation. Either way, the installed Visit Book app can run without Codex or VS Code being open.