Thanks guys ^_^ I hope he plays out well in the rp.

Kings Cross station is a train/tube station in London (It exists in real life! Do a quick google for more info and history). Platform 9 3/4 is the secret-magic platform (Between platform 9 and 10) in Kings Cross that muggles can't get into. That is where the Hogwarts Express departs from. 

Hope that answers the question.