Welcome to KnittingHelp! Over and under are referring to the way you'll twist the two yarns in making this pattern. If you let both yarns dangle down from the knitting, you can see that you can cross the yarns in two ways: the first strand over or across the front of the second the second strand, the first strand under or behind the back of the second. The only comparable video
I can think of is one that shows the way you cross yarns for intarsia. The yarns are crossed at the back of the work in this case but the idea of crossing the yarns is the same. Of course it looks like you'll be crossing yarns more frequently in your pattern. It's a great looking hat, btw.