How to order in japanese at a japanese restaurant?

ok, so im going out to eat with my family tonight. i am studying japanese, and i really want to order in japanese. i hear the people in the kitchen talking in japanese, but how should i know if the waitress/waiter speaks it? do i just ask if i can try to order in japanese? and how would i do it? do i say: 私は2つの6ピースカリフォルニアロールはしてください必要があります (I will have two six piece california rolls please)? and how do i say the numbers? i always forget. anata wa domo arigato.