Author: Claude AI, under the supervision, prompting and editing by HocTro
Opening
The previous six articles took you from "what is a token" to "the enormous buildings where AI lives." You understand how AI reads tokens instead of words, how your message travels through APIs and HTTPS, how AI guesses each token by probability, how neural networks learn through billions of adjustments, and how all of that runs on thousands of GPUs inside data centers that consume power like small cities.
Now comes the practical part.
Claude Code is one of the most powerful ways to use AI — not through a website, not through a mobile app — but right inside your terminal (command line window). It can read your files, write code, run commands, and work directly with your project without you copying and pasting back and forth.
This article walks you through every step: what Claude Code is, how to install it, and how to get started.
What Is Claude Code — And How Is It Different From Claude on the Web?
When you use Claude at claude.ai, you're using a web interface: type into a chat box, receive an answer, copy what you need, paste it somewhere else. Useful, but there's a gap between the AI and your actual work.
Claude Code eliminates that gap. It's a CLI (Command Line Interface) — a program that runs inside a terminal, where developers and technical users work every day. When you open Claude Code inside your project folder, it knows that project — it can read the entire file structure, understand the code you're writing, edit files directly, and run commands right there in the same terminal.
Practical examples:
- You have a Python script with an error — Claude Code reads the file, finds the bug, fixes it directly, no copy-pasting needed
- You want to add a feature to your web app — Claude Code reads the entire codebase, understands the architecture, then writes new code that fits
- You need to understand a project someone else left behind — Claude Code reads all the files and explains them to you
The core difference: Claude on the web knows about code. Claude Code works with code.
What You Need Before Installing
To install Claude Code, you need to look up to their site for the latest instructions.
https://code.claude.com/docs/en/quickstartYour First Claude Code Session
Open your terminal, navigate to your project folder (or any folder you want to work in), then type:
`
claude
`
Claude Code starts up and shows a prompt waiting for input. You're now in a working session — like a chat, but the AI knows the context of the folder you're in.
Try a few simple things right away to get a feel for it:
`
What files are in this directory?
`
Claude Code will list the folder contents and explain the structure.
`
Read the README.md file and summarize it for me.
`
Claude Code reads the actual file and responds based on real content — not guessing.
`
Write a simple Python script that reads a CSV file and prints the number of rows.
`
Claude Code writes the script, asks if you'd like to save it to a file, and saves it if you say yes.
What Claude Code Can Do Right Away
After installation, you can use Claude Code for a wide range of tasks without learning anything extra:
Read and explain code:
`
Explain this main.py file to me — I don't understand its structure yet.
`
Find and fix bugs:
`
This script is throwing a "KeyError: 'name'" error. Help me find what's wrong.
`
Write new code:
`
Add a /health endpoint to app.py that returns {"status": "ok"}.
`
Run commands and interpret results:
`
Run git log --oneline -10 and explain what the recent commits are about.
`
Work with documentation:
`
Read all the .md files in this folder and write a combined summary.
`
Refactor code:
`
This function is too long. Help me split it into smaller functions that are easier to read.
`
Tips for Getting Started
Be specific, not vague. "Fix this bug" works less well than "File login.py line 47 is throwing a TypeError — help me understand why and fix it." Claude Code performs best when you give it enough context.
Don't hesitate to ask for more. If Claude Code finishes an explanation and you still don't follow, just say "Explain that part again" or "Give me a more concrete example." It doesn't get impatient.
Review before you approve. When Claude Code suggests running a command — especially one that might modify files or system state — read the command carefully before agreeing. Claude Code asks for confirmation; don't click through automatically.
Use CLAUDE.md to give standing instructions. Claude Code automatically reads a file named CLAUDE.md in your project folder if one exists. This is where you write fixed instructions: what language this project uses, naming conventions, which folders should never be modified. Write it once and Claude Code remembers across every session.
Start small. For your first session, don't try to hand it an entire large project. Start with one file, one function, one specific question — to understand how it works before trusting it with more.
Exit with /exit or Ctrl+C. When your session is done, type /exit or press Ctrl+C to close Claude Code.
Claude Code Is Not Magic
One important thing to keep in mind: Claude Code is very capable, but it's still AI — meaning it can still be wrong. Especially when:
- Code is complex with many dependencies and side effects
- Your request is ambiguous — it guesses your intent, and sometimes guesses wrong
- The task requires specific business knowledge that only you have
Use Claude Code like a very capable collaborator, not as something that completely replaces your judgment. It often writes code faster than you can — but you still need to understand what that code does and verify that it's correct.
End of the Journey
Seven articles, seven questions, one journey from the inside out:
- Article 1: AI reads tokens, not words
- Article 2: Your message travels through HTTP, an API, and streams back to your screen
- Article 3: AI guesses each token by probability — and sometimes confidently makes things up
- Article 4: Neural network + attention mechanism + scale = genuine capability
- Article 5: Three training stages: pretraining, fine-tuning, RLHF
- Article 6: Data centers — real buildings, real electricity, real GPUs
- Article 7: Claude Code — putting all of it in your hands
AI is no longer a black box. You know what it does, how it does it, and now you have the tool to use it at a genuinely powerful level.
Enjoy exploring!
Quick Reference Table
| Command / Concept | What It Does |
|---|---|
npm install -g @anthropic-ai/claude-code |
Install Claude Code for the first time |
claude --version |
Verify the installation succeeded |
claude |
Start Claude Code in the current directory |
ANTHROPIC_API_KEY |
The environment variable holding your API key |
CLAUDE.md |
The file where you write standing project instructions |
/exit or Ctrl+C |
Exit the current Claude Code session |
| console.anthropic.com | Manage your account, API keys, and credit balance |
Key Things to Remember
- Claude Code runs in the terminal, not the browser. It reads real files, runs real commands, and works directly inside your project.
- You need an API key and credit in your Anthropic account. Not free — but affordable for individual use.
- CLAUDE.md is permanent memory. Write your project instructions there once and Claude Code remembers them across all sessions.
- More specific prompts get better results. Detailed context = more accurate responses.
- Review before approving important commands. Claude Code asks for confirmation — don't skip that step.
- You've completed the full series. Token → Server → Token generation → Neural network → Training → Data center → Claude Code. Well done!