Welcome to shotgunning from a fellow novice! I got an 870 last week and shot it yesterday for the first time with no experience or advice other than what I'd read on TFL. DO read the thread Dave mentions above on Proper Mounting Techniques; and while you're at it, or when you have time, do a search for threads Dave has started--there are dozens, on a variety of topics of interest to shotgunners--and read them all. You'll enjoy yourself and learn a good bit.
I don't know what your shooting experience is like, but I don't have a lot of big-bore long-gun background, and some of the discussion of recoil from the mighty 12 gauge had me a bit nervous before shooting yesterday--but there's good news. If you position yourself and gun close to correctly, that 'shove' from light loads or even from a reasonable load of buck is a blast. You'll surely know you've shot something, and after 50 shells I could feel new and strange feelings in my shoulder this morninng; but I'm persuaded that folks who make a mountain out of recoil must be doin' something wrong.
So--read up, go shoot, and have fun!