Do i fill up my ability tree and strong medium and weak abilities? And then what do i do on the RP board do i say like.... Xavior walked into ishbal and saw a car ex.?

Yes, you have to fill in all the character's weak points and strong points on the guidelines. As for the actual RP, you can make it any type of style you wish.

Ex: Xavier, while traveling down the city of Dublith, found himself face to face with a State Alchemist. "Oh it's you..."

Or it can be more mechanical, as long as its detailed and you know what's going on.

Ex: Xavier, while traveling down the city of Dublith, found himself face to face with a State Alchemist.

Xavier: "Oh it's you..."

It can be any style you wish as long as its detailed, clear and understandable by others.

I have a question, Where are the guidelines for making RP characters, i can't seem to find them, or do they not exist?

Here they are!

It's in the RP Handbook section. A bunch of other stuff is there too...

I wuz asking about what 2 fill in. But thnx anyway XD... i just made something up 4 it like this...Right Here