Starting Claude Code Sessions

Welcome back to Foundation — Getting Started with Claude Code! You have completed the first unit, in which we explored what Claude Code is and how it differs from traditional AI tools. Now, in this second unit, we are ready to actually use Claude Code for the first time.

This lesson focuses on the basics of interacting with Claude Code: how to launch it, send messages, and manage your sessions. These fundamentals might seem simple, but mastering them will make you comfortable and efficient when working on real development tasks. By the end of this unit, we will be confident in navigating the Claude Code interface and ready to tackle actual coding challenges.

Before we launch Claude Code, let's take a moment to understand where we will be working. Claude Code operates entirely within the terminal, also called the command line or shell. This is the text-based interface where we type commands and see results.

If you are new to working in terminals, do not worry. Using Claude Code does not require advanced terminal skills. The terminal is simply where we start Claude Code and where it displays its messages. Think of it as opening an application, but instead of clicking an icon, we type a command.

For macOS and Linux users, the terminal application is typically called Terminal. Windows users can use Command Prompt, PowerShell, or Windows Subsystem for Linux (WSL). Once you have a terminal window open, you are ready to begin.

Starting Claude Code is straightforward: we simply type claude in our terminal and press Enter. This single command is all it takes to begin a session.

Note: The first time you launch Claude Code after installing it, you will be prompted to authenticate. Follow the on-screen instructions to log in with your Anthropic account. Once authenticated, you will not need to log in again unless you explicitly log out.

Let's see what happens when we launch it:

╭─── Claude Code v2.0.42 ────────────────────────────────────────────────────────────────────────────────╮
│                                    │ Tips for getting started                                          │
│            Welcome back!           │ Run /init to create a CLAUDE.md file with instructions for Claude │
│                                    │ ───────────────────────────────────────────────────────────────── │
│               ▐▛███▜▌              │ Recent activity                                                   │
│              ▝▜█████▛▘             │ No recent activity                                                │
│                ▘▘ ▝▝               │                                                                   │
│                                    │                                                                   │
│   Sonnet 4.5 · API Usage Billing   │                                                                   │
│        /usercode/FILESYSTEM        │                                                                   │
╰────────────────────────────────────────────────────────────────────────────────────────────────────────╯

───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
> Try "refactor <filepath>"
───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  ? for shortcuts                                                                                     Thinking on (tab to toggle)

The welcome screen displays several pieces of information. We see the version number (v2.0.42), a greeting, and importantly, which Claude model is being used (Sonnet 4.5). The billing information tells us how our usage is being tracked. The > symbol at the bottom is the prompt where we type our messages.