You play em like any other card. The 4 is loyalty counters. You manipulate them by using the abilities the planeswalker has (+1 gives him a loyalty counter, and the -8 takes away 8, and you can't activate any ability you don't have the counters for). The opponent can target them just as they do players though, so monsters can attack them directly, taking away loyalty counters, unless you wish to block.
---------- Post added 2013-01-05 at 03:23 PM ----------
He's not as vile as Jace, the Money Scalper I was talking about before, but he's still decent.