It's hard to tell but u-turning is letting go of accelerate, holding square, and holding down+left/right. This soothly turns you like a handbreak turn without losing speed.
Air breaking is where you're in the air and you let go of accelerate, hold square, turn to face the direction you want, then press accelerate again to jolt yourself forward (all before hitting the ground).
If you try it yourself you'll notice the "jolt" much moreso, the example in the webm is really good so you don't notice it as much.
