How to Use Claude Code: Complete Beginner's Guide

You can skip Stack Overflow. Claude Code lets you talk to your codebase like it's a senior engineer sitting next to you. Ask it to refactor, debug, write tests, or explain legacy code. It works in your terminal, sees your entire project, and remembers context across sessions.

This guide walks you through installation, your first project, common commands, debugging tips, and one pro trick most people miss.

What Claude Code Does

Claude Code is Anthropic's command-line AI coding assistant. Unlike the web chat interface, it lives inside your terminal and can read, write, and execute code in your local project. It uses Claude 4 Sonnet under the hood and connects directly to your file system.

The key difference from chat: Claude Code sees your folder structure, can run git diff, execute test suites, and modify files in place. It does not just suggest code. It writes it, runs it, and fixes errors.

Installation (5 Minutes)

You need Node.js 18 or higher. Check your version:

``bash

node --version

`

Install Claude Code globally:

`bash

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

`

Authenticate with your Anthropic API key:

`bash

claude-code auth

`

Paste your API key when prompted. You can get one from console.anthropic.com. Claude Code costs $0.03 per 1,000 input tokens and $0.15 per 1,000 output tokens. A typical session runs $0.50 to $2.00 depending on project size.

Verify the install:

`bash

claude-code --version

`

You should see something like claude-code/0.8.2.

Your First Project

Navigate to any project folder and launch Claude Code:

`bash

cd ~/projects/my-app

claude-code

`

Claude Code indexes your codebase on first launch. For a medium-sized React app (around 200 files), this takes 15-30 seconds. You will see a loading bar as it scans files.

Once ready, try your first prompt:

`

Explain what this project does and list the main entry points.

`

Claude Code will analyze your package.json, README, and key files. It gives you a concise summary. No more guessing what src/utils/legacyHelpers.js does.

Now ask it to do something:

`

Add error handling to the API calls in src/api/client.js

`

Watch it read the file, identify the fetch calls, wrap them in try/catch blocks, and write the changes back. It will show you a diff before applying.

Common Commands You Will Use Daily

Explain Code

`

What does this function do? Show me the file: src/components/DataTable.tsx

`

Claude Code reads the file and explains the logic in plain English. It traces imports and dependencies automatically.

Refactor

`

Refactor this class to use hooks instead: src/components/OldClass.jsx

`

It rewrites the component, preserves functionality, and updates imports. You review the diff, then approve or reject.

Write Tests

`

Write unit tests for src/utils/calculator.js using Jest

`

It creates src/utils/calculator.test.js with edge cases, mock data, and assertions. If your project uses Vitest or Mocha, tell it explicitly.

Fix Bugs

`

The login form throws "undefined is not iterable" when submitted. Find and fix it.

`

Claude Code searches the error message, traces the stack, identifies the variable causing the issue, and proposes a fix. It does not guess. It reads the code.

Generate Boilerplate

`

Create a new Express route handler for user profiles with GET, PUT, and DELETE

`

It scaffolds the file, adds validation, and wires it into your existing router. You specify the database layer (Prisma, Mongoose, raw SQL) and it adapts.

Run Shell Commands

`

Run the test suite and tell me which tests are failing

`

Claude Code executes npm test, captures output, and summarizes failures. It can re-run with npm test -- --verbose if you need more detail.

Debugging Tips That Save Hours

Use @ to reference files. Instead of pasting code, type @src/utils/auth.js and Claude Code loads it automatically. This preserves context and avoids truncation.

Chain commands. After a refactor, follow up with:

`

Run the linter and fix any style issues in the files you just changed

`

Claude Code remembers what it modified and runs eslint --fix only on those files.

Ask for alternatives. When Claude Code proposes a solution, ask:

`

What are two other ways to solve this? Include tradeoffs.

`

This prevents over-reliance on one pattern and teaches you edge cases.

Use /compact for large projects. If your repo has thousands of files, add /compact to your prompt. Claude Code summarizes file contents instead of reading full files, keeping token usage reasonable.

Set custom rules. Create a .claude-code.md file in your project root with style guidelines. Claude Code reads this automatically and follows your conventions. Example:

`markdown

Claude Code Rules for This Project

  • Follow the existing file naming convention (kebab-case)

`

The Catch: What Claude Code Does Not Do Well

Claude Code cannot replace architectural decisions. It writes code based on patterns it sees, but it does not know your business constraints, compliance requirements, or long-term roadmap. If you ask it to "redesign the database schema," it will produce a plausible schema that might not fit your scale or regulatory needs.

It also struggles with proprietary frameworks. If your company built an internal UI library with no public documentation, Claude Code treats it like a black box. It guesses based on usage patterns in your codebase, but those guesses miss edge cases.

Token costs add up. A 2-hour session on a large codebase can hit $10-15. For bootstrapped startups, this is real money. Budget accordingly.

Security is another concern. Claude Code has file system access. If you accidentally run it in a folder containing .env files with production keys, it reads them. It does not exfiltrate data, but the tokens travel to Anthropic's API. Keep it out of directories with unencrypted secrets.

One Pro Trick: Context Sessions

Most users treat each prompt as isolated. Claude Code supports session history. Press Ctrl+S to save the current session, then resume later with:

`bash

claude-code --resume

`

This preserves the full conversation, file modifications, and decisions from your last session. You do not re-explain the project every time you open it.

Better yet: name your sessions by feature.

`bash

claude-code --session "auth-refactor"

``

Now you can have parallel sessions for different branches. Work on authentication in one window and UI cleanup in another. Claude Code maintains separate context for each.

The Bottom Line

Claude Code turns your terminal into a senior pair programmer. It reads your codebase, writes production-ready code, runs tests, and explains legacy systems. The learning curve is shallow if you already know the command line. The real skill is asking precise questions and reviewing diffs critically.

Start with small tasks: explain a file, write a test, fix a bug. Graduate to larger refactors once you trust the output. Set a daily spending cap in your Anthropic dashboard to avoid surprise bills.

You can skip Stack Overflow. But you still need to think.

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