installing claude code

installation

Claude Code is Anthropic's coding agent running in the terminal. It installs via Node.js, with a single command:

npm install -g @anthropic-ai/claude-code

The -g flag means global installation (the package installs for the whole machine, not one project – you can start it from anywhere). If the command fails with a permission error, don't run it with sudo – fix the npm directory permissions instead (the error message links to the solution).

Check:

claude --version

If it prints a version number, you're done.

signing in

Enter any project folder (or create one) and start it:

mkdir test-project && cd test-project
claude

On first start you sign in to your Anthropic account in the browser – this connects the terminal to your subscription. After that, a conversation-like interface greets you in the terminal: this is where you type the tasks.

the first command

Try it with this:

Create a hello.txt file that introduces you in one sentence.

Watch what happens: Claude Code shows what operation it wants to perform (writing a file), and asks for approval before touching anything. This is the default, safe mode – stay on it as a beginner. Enter approves, Esc rejects.

three settings for day one

1. CLAUDE.md – a text file living in the project root that the agent reads at the start of every session. This is where you write the project's rules ("comment in my language", "always run the tests"). It is your most effective tool for steering the agent – a whole lesson covers it later.
2. /help – issued in the conversation, it lists the commands. Commands starting with / control the tool; they don't go to the model.
3. Have Git in the project. Before giving the agent real work, run: git init && git add -A && git commit -m "starting point". That way every agent change is reviewable with a git diff, and you can always roll back.

Rule of thumb for the first weeks: the agent may write anything, but you do the committing. The commit is your quality gate.

if you get stuck

• claude --version doesn't run → the Node.js install is incomplete; revisit the system requirements lesson.
• Sign-in error → check that your subscription is active in the claude.ai settings.
• The terminal wraps strangely → try iTerm2 (macOS) or the Windows Terminal instead of the built-in one.

In the next lesson, Codex goes on – the second agent, with different strengths.