PLEASE HELP, everytime i talk to a boy i make a fool outta myself!?

okay im 15 and i barely talk to boys! i mean they think im hot but im to shy to talk to them! like i always embaress myself, i never keep my cool and i freak out! i never dated/kissed someone but i look like i did. i really wnat a boyfriend but i can never have a decent conversation. i usually avoid guys i like then when they like me i say i like someone else. and remeber i freak out! haha thanks, i know i sound like a loser;p but please tell me what to say,do,flirt anything!