Claude Code offers a broad variety of configuration options and slash commands. You'll, of course, see all crucial commands throughout this course.
One command you should be aware of right from the start is the /model command which let's you choose the AI model you want to use.
Typically, you'll only change this from time to time, if at all. But you should at least initially check that you're working with the AI model you want to use (e.g., "Opus", the most capable AI model offered by Anthropic).
You can also change the model by using the OPTION + P (macOS) / ALT + P (Windows, Linux) shortcut.