How does this work???

Alright, I've recently reached level 30 and discovered the world of ranked teams. I have been looking around and I have seen several team sites, each one with multiple ranked teams. My questions are: how do most people do this? Are players interchangeable? Is it a set 5 per team or do you have a player rotation? Why do these groups own multiple teams? Does the whole group get rewards? A link to a helpful site or a full-blown explanation would be appreciated.