Install Claude Code with the official installer. The exact command depends on your system and changes over time, so use the source of truth: the quickstart at code.claude.com/docs/en/quickstart. Copy the one-line install command for your system into the terminal and press Enter.
Then, inside your project folder, type claude and press Enter. First run opens your browser to sign in with your Claude account (a paid plan is required, see what this costs). After that you land at a prompt where you type in plain language.
Install, run claude in your my-first-app folder, sign in, then type "hello" and see it answer. Type /help to see what commands exist. You are now a person who uses a terminal.
The install command fails or prints something scary? Do not debug from memory or an old video. Go back to the quickstart page, copy the exact command for your system again, and read the first line of the error: most of the time it names the fix. Still stuck? Paste the whole error into claude.ai and ask what to do.
Done when: claude runs and answers you.