I want to give coding AIs a fair shot, where do I start?

I use VSCode and for the past few months the release notes have been largely about AI features. I use Copilot to autocomplete some code (the passive tab autocomplete feature) and sometimes generate unit tests with right click->Copilot->Generate tests. That’s it. I also use ChatGPT on the side to discuss higher level decisions or to understand some stuff I don’t know about in details.

I know there are many more features (chat, agent mode, MCP, add files to context…) but I struggle to understand how it works and how to integrate it in my flow.

How do you use AI on an existing codebase? I work on a monorepo with ~15 microservices, how to make it understand how it works? How do you give it more context? What am I missing on and what can I try?

I have a surprisingly hard time finding good and recent resources actually explaining what to do in a real, professional context, beyond generating a todo app from scratch.