Hitting the g-spot

I want to try fingering my girl friend some time soon and I want to make it as pleasurable as possible for her. I've heard that I can massage her G-spot while licking her clit and that will drive her absolutely nuts with pleasure.

How do I find the g spot, apparently it's about 2 inches into the vagina and on the upper wall. Will it be obvious when I hit it, like does it feel different or will she immediately react?

Also about how long will it take for her to have an explosive orgasm after I start? 5 minutes, 10 minutes? longer?

Thanks

>>10
Actually I bet most 15 year old guys think like him.

Scratch that. Most guys up until their 30's think like this. "zomg, a gurl can do moar than just lie their on dah bed??? y didnt i think of dat!!11"