You just press the left and right triggers. Its a mini-game you unlock in the computer. I haven't done it yet. I'm sure there are loads of links on the internet.
Started and completed the campaign yesterday- wow I thought it was brilliant although the plot was OTT like MW2 again. But it was great nonetheless. Great visuals, excellent facial animation, great action sequences, varied locales and some pretty tense encounters. Oh and it has Ice Cube and the lead from Avatar lending their voices- what more can you want!
On the MP side of things- they still haven't sorted out the whole issue with your party joining games etc. But yeah- I've already got the Attack Dogs and the Chopper several times. Its definately growing on me. I think the maps are the biggest let down.