What Claude Code is, and installing it

What you’ll be able to do

By the end of this lesson Claude Code will be installed and signed in, and you’ll have asked it a first question about a real folder on your machine.

Agentic coding in one paragraph

A chat assistant answers from what you paste into it. Claude Code works inside your project. It can list and read files, search the codebase, run commands such as tests or builds, and edit files. It does this in a loop: it takes an action, reads the result, and decides the next step until the task is done. Actions that change things ask for your permission first, so you stay in charge.

That changes what you ask for. You stop asking “how would I write this function?” and start asking “add input validation to the signup form and make sure the tests pass.”

Step 1: Check the prerequisites

You need:

• A terminal: macOS Terminal, Windows Terminal/PowerShell, or any Linux shell
• A Claude account with Claude Code access: a Pro, Max, Ultra, Team or Enterprise plan, or a Claude Console account with API billing. The free claude.ai plan doesn’t include Claude Code.
• Git. Claude Code works without it, but every lesson in this course assumes it. On Windows, Git for Windows is optional: without it, Claude Code runs commands in PowerShell.

Prefer a graphical app? Claude Code also runs in the Claude Desktop app (macOS, Windows, Linux beta), in VS Code and JetBrains (lesson 4), and in the cloud at claude.ai/code. This course uses the terminal because everything else builds on it.

Step 2: Install

Use the native installer for your platform.

macOS / Linux / WSL

curl -fsSL https://claude.ai/install.sh | bash

Windows (PowerShell)

irm https://claude.ai/install.ps1 | iex

Windows (CMD)

curl -fsSL https://claude.ai/install.cmd -o install.cmd && install.cmd && del install.cmd

The native installer updates itself in the background. Package managers work too, but you update them yourself: brew install --cask claude-code (macOS), winget install Anthropic.ClaudeCode (Windows), or npm install -g @anthropic-ai/claude-code (needs Node.js 22 or later, and never sudo).

Tip: Piping a script into your shell runs it with your permissions. That’s normal for installers from a vendor you trust, but get into the habit of opening the URL in a browser first to see what it does.

Step 3: Start it and sign in

Open a new terminal so it picks up the updated PATH, then:

claude --version
claude

The first run walks you through signing in with your Claude account in the browser. When that’s done you’ll see a prompt waiting for input.

Step 4: Ask your first question

Quit for now with Ctrl+C twice, or type /exit. Then cd into any project you have, even a small one, and start Claude Code there:

cd ~/code/some-project
claude

Ask:

What does this project do? Give me a 5-bullet summary and point out the main entry point.

Watch what happens. Claude doesn’t guess: it reads files first. You’ll see tool calls such as listing directories and reading files go by before the answer appears.

Verify it worked

• claude --version prints a version number
• You signed in and reached the interactive prompt
• Claude summarised a real project, and you saw it read files to do so

Common problems

Symptom	Fix
command not found	Open a new terminal. If it still fails, add the install directory the installer printed to your PATH.
Anything else	Run claude doctor. It checks your installation and settings and suggests fixes. Inside a session, /doctor does a full checkup.
The token '&&' is not a valid statement separator	You’re in PowerShell, not CMD. Use the PowerShell command.
Browser login doesn’t come back	Copy the URL shown in the terminal into your browser by hand.
Corporate proxy errors	Set HTTPS_PROXY in your environment before starting claude.

Next: what actually happens when you give Claude a task, and how to stay in control of it.