Parce que, Puisque, et Car
Parce que = because
J'etais en retard parce que j'ai manque le bus = I was late because I missed the bus
Puisque = since
You can leave, since you're sick. = Tu peux partir puisque tu es malade.
Car = for
Car is a coordinating conjunction, should not begin a sentence.
David isn't coming, for he is at the university = David ne va pas venir, car il est à l'université.