He approachs you, he will stay close and glance at you, in a position I've been in the guy put his SnapBack on me. He could even whisper a compliment like ...hey beautiful.
Apart from that ^ he will also constantly fins a way to talk to you or stay close to you.
If he trys to dance by u or asks to dance w/u
He could come up to and just start generally dancing. If he starts to come closer and closer he may be into you. This also includes an grinding.
If you see that he is dancing close to you and sometimes he holds your hand or something, he likes you. But if he is secretly drifting off while dancing, then probably he doesn't want to be with you
Ask him to go with you to the party
if he still wants to hang out with you Eg: the park, the movies, a party, anywhere.
He will tell you he likes you or will ask you to do something with him (go for coffee, see a movie, go to a party together).
iam in love with this guy but i do not know if he likes me or some other girl
when he says he likes you.
If a guy likes you but you don't know him he may look at you or walk by you whenever possible.
http://www.wikihow.com/Know-if-a-Guy-Likes-You
Not sure how you expect someone to magically know something.
Pitbull
It is ok to like a guy after you know he likes you. That is perfectly normal and a part of life.
You ask the guy.