when u donīt know how to act

First think about how he is:
If he is confident, then act confident around him, not too much though as he might be thinking differnt things about your confidence. If he gets full on then talk to him donīt do anything that makes you feel uncomfortable.
If he is shy, then donīt be over the top as he might be scared, just talk to him with confidence yet hold back a bit until he starts up. Shy boys are always hard to get along with, as they donīt know what to do, so make the first move and you may be suprised.