If you're buying the factory "Nudge Bar Garnish" then it will come with a step by step instruction sheet. There's not much to it. Basically you take the front bumper out, enlarge the holes where the number plate bolts are, install the brackets and bolt it all up.
If you want a primer on taking the front of the car off, I wrote up this a little while ago:
I don't know who you're buying the bar from or how much you're paying, but I know retail is about a grand for those things. The only real benefit they offer is a reasonable under-body guard at the lip which gives some lead-in protection and a good mounting platform for additional spotlights. Other than that, they don't offer much.
Considering their cost, I'd opt for a mild spring lift, underbody protection plates or a set of AT tyres before buying that. If you're planning serious off-road adventures and would like the opportunity to fit a winch, save up for an ARB bull bar instead.