A is the Clitoral Hood. - This is the cover to the clitoris. Sometimes the clit likes to hide under this. It is also sensitive and can be stimulated when the clit hides.
B is the clit. - This is a highly sensitive area thats sole purpose is for stimulation and pleasure.
C is the urethra. - It's obvious what that does.
D is the inner labia. - These cover the vaginal opening. They are sensitive and are good for stimulation as well. This is a teasing area though so don't spend too much time there.
E are the outer labia. - They are sensitive but more so when bare (no hair). They are the outer/visable part of the vagina and are sometimes referred to as the "lips".
F might be pointing to the hymen. - This is the thin membrane that is present on some virgins. It can be broken while riding a bike and some girls aren't born with them so it isn't an accurate indicator of whether a girl is a virgin or not. If it's still intact when you first have sex with a girl, it will tear and there could be some minor bleeding. This is why a lot of women say there first time was painful.
G and H are pointing the area right around the vaginal opening. - It's kinda obvious what you can do with the hole itself.
I is the anus. - It is also sensitive and sexually satisfying but some women don't like this kind of touch. Just make sure she's into it before you go near this.
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The g-spot and the clit are two seperate things. The clit is outside the vagina (just above the opening) and the g-spot is inside the vaginal opening.
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As for the g-spot...
To locate the g-spot, you insert two fingers (with your palm up) a couple of inches inside the vagina and you make a "come hither" motion. Just do that until your girl says you've got it or you see her react with pleasure. She may feel a sudden urge to pee but assure her she wont. It's just a sensation because of the close proximity of everything. Just rub gently and be gentle at first. Some women don't enjoy this so don't be surprised. Some women don't really even react to this. A little hint. It's a lot easier to hit it if you put yourself between her legs rather then doing it while you are next to her. You can get in deeper. Another good position to do this in is the "doggy style" position. You can insert your fingers much deeper and you can stimulate everything a lot more and a lot easier. Let me know if you have any more questions.