What are the rules?

That’s exactly what the books are for. There are free versions with the basics online that will explain precisely how the game is played. Beyond that? It really comes down to the group and setting. Everyone kinda has their own in-house stuff, and there are tons of settings both official and unofficial that can change a lot about the game beyond the core mechanics.

Read the Player’s Handbook and watch some streamed sessions and you’ll have a better understanding than what could be told via a text post.