Any pointers for making a game mode?

[ezra]

I've been wanting to make a simple combat game mode, as I have lots of prior experience (5 years to be exact) with Lua and a small amount of experience with SLADE. The main issues I'm having are:

1. Knowing how to structure an addon
2. How game modes even work
3. How the server and client communicate with a single pk3

Hopefully someone's willing to share some knowledge! Thanks in advance.