Go buy a sex book, or, check out
www.sex-project.com (I think I got that right), they will have some detailed 'guides' for you.
Don't be too embarassed to go to the bookstore or library and check out a few sex-books...the how to kind. They are very usefull, they help dispel a lot of myths about sex, and give you a good idea of what exactly you are supposed to do, when, and where to do it.
BTW, don't try to stick your head in your girlfriends crotch just after you manage to get your fingers down there. Also, be gentle, and listen to any 'hints' she leaves about what you should be doing, and if you are really lost after you get your hand down there, ask her what to do.