How do you ask you girl out in spanish?

Probably the best way to get the desired message across is "Él me invitó a salir". "He invited me to go out". The examples below are more "will you be my girlfriend", which is not really the same thing.

No idea, that's a funny English thing that we say. You could say 'El me quiere a ser su novia' which means 'he wants me to be his girlfriend'. However, I think su is possessive which means that it might imply ownership, so it would sound funny but get the meaning across somewhat.

i speak spanish too and i think that

el me quiere a ser su novia is correct..

well it means the same thing