It's important to understand that you need to drag, or slide, those back wheels around. They need to be touching the ground. Don't just do a kickturn, or it won't work, and you'll end up either flying off to the side or just wiping out.
Once your board is sideways, you want to lean back some. Push out with your feet, sliding the board along the ground.
As your speed is spent in the slide, you will stop, and you should end up just standing on your stopped board! The first several times you try to powerslide, you might need to do some kickturns to keep your balance, but the goal is to get to the point that you won't need to at all.
