Imagine there are 5 slots A through E
Slot A can be filled with 5 choices
Slot B can be filled with 4 choices (once you pick a movie you can't pick it again)
Slot C has 3 choices
Slot D has 2 choices
Slot E has 1 choice
In total, there are 5*4*3*2*1 = 120 different ways to order the movies