Marine and Army are skin tight on the sides and a little at the top (called a 'high and tight'). Navy is more just a normal short clean cut haircut.

Tapered and block is about the back of the head. Blocked is trimmed close at the back but then squared off at the bottom of the back. Tapered is trimmed close and then just tapered down until it disappears in the back.

I'd send pictures but it is so hard to do that here.