Explain this codebase like I just joined

I'm new to this codebase. Files/context below:
[paste key files or a tree]

Walk me through it like I just joined the team:
1. What does this app actually do, in two sentences?
2. The main entry points and how a request flows through.
3. The 5 files I should read first, and why.
4. Any patterns or conventions I should copy.
5. Anything that looks risky, confusing, or likely to bite me.

Be specific and cite file names. If something is unclear, say so instead of guessing.