I just recently started watching Online Piano and Violin Tutorials on Youtube.

In one of her lessons, she said using the right hand, you should play a C scale by 1, 2, 3, 1, 2, 3, 4, 5.

My question is: Suppose I am playing a C, should I always use my thumb(1)? I still can't grasp what finger is used to hit what piano key. Is there a predetermined rule that for example index finger(2) is always used to hit D?