I've been longboarding for like 7 years, back when Sector 9 boards were still like 80 bucks. Anyway, powersliding is easy, that first guy explained it well. Just watch out for sand and shit cause you might end up on your back.
If you have a longboard, not a shortboard, i suggest loosening the trucks all the way if you are into carving, which is definately the best part about longboards. You can still do ground tricks, just takes a while to get down the balance. Powersliding works better with tighter trucks, but that is the only benefit of it.
Invest in some abec 7s, you will fly. I've been clocked going 30mph on my board before. Fun times man.
We'll have you dead pretty soon.