Sure thing! I'm Mint and this is the Warrior Cats RP Forum.
So there are several things you can do here. If you click on Home, all those different links might look a bit intimidating, but I promise it all works out. This is a forums that's primarily to chat and interact with other users over the common interest of Warriors. It also has a very prominent RPing community. I go into more detail below or you can take that as a TL;DR.
There's Warriors General, where you can discuss the Warriors books in all their aspects. Favorite cat you wanna gush about? Go here. Have a beef with how a Clan was written in the latest book? Go here. Want to find spoilers? Go here. All spoiler threads are marked, so you can avoid them if you want to as well.
Then there's Warriors Fan Clans, where you can RP (roleplay) as a cat in a clan. If you're unfamiliar with what RPing is, it's where you write a very small part of a story from a cat you created's point of view. Something like: Squirrelpelt hated to see his sister so mad, but he had to agree - the NightClan leader was being unfair.
Add more sentences as you like, since RP posts vary in size. If you don't want to join an existing Clan, you can always make your own!
Warriors Fan Fiction - or the WFF - is one of two writing communities, and the largest, on the forums. Very warm and welcoming, the WFF is where different users write and post stories which take place in the Warriors universe. Many of the writers also write original works - including one who is a long time published author - so if you wanted to check it out that's often where I hang out as well.
Then there's Off-Topic Roleplaying. That's much like Fan Clans, only it's for roleplays for things other than Warriors. Harry Potter RPs, Percy Jackson RPs, things like that.
Art Forum is where the art community hang out. As well as the comic creators. So if you wanted to read some Warriors fan comics, you'd look here.
Off Topic Discussion is one of the largest boards for user activity and it's where all the silly talking goes on. Bunch of chats, on really whatever comes to mind.
There are of course other boards, but those are the most frequented.
Hope that helps? If you have any questions, don't be afraid to give a shout.