Sure, action points are awesome. You use them to make extra attacks or you're totally wasting them.
Ok, real explanation. Action points are awesome. You are set to 1 after an extended rest no matter how many/few you had before. You gain 1 every milestone (two encounters (combat or otherwise) in a row without an extended rest). You can use them to gain an extra action of any type during your turn (I think it's only during your turn, would be amusing to see someone use one for an extra opportunity or reaction though). You may only use 1 per encounter. A lot of paragon paths add effects/alternate uses to the use of action points, as do some classes I believe, and feats. Typically
though you use them for a second standard action (the type of action most attacks are) in combat.
Edit: It keeps surprising me how much Mountain wishes to say. My original intent for him was to have very little dialog. Admittedly this isn't a ton or anything but, he's saying about twice as much as I was expecting.