Hi.
How nice that your boyfriend wants to know where your G-spot is; that probably means he's truly interested in your pleasure, and well-informed too. Now it's your turn to find out what all the fuss is about.
The G-spot is a highly errogeonous zone of nerve endings that can usually be accessed by inserting a finger (let's start there) a couple of inches inside the vagina toward the pubic bone. Many women report intense pleasure when this quarter-sized area is rubbed or otherwise stimulated. Along with the clitoris, the G-spot has attained high status as being one of the main conduits to female pleasure.
The "spot" is named for the physician Ernest Grafenberg who "discovered" it back in the 1950s, although you have to figure that someone had "discovered" it before and just hadn't bothered to name it. Since the area is located behind the pubic bone, in front of the urethra, having the area stroked sometimes makes women feel as though they have to pee. Some women do release a liquid through the urethra when stimulated this way, but the liquid is not pee. Chemically, it's similar to the liquid men ejaculate, except there is no sperm.
To find yours, try practicing on yourself first, but don't get discouraged if you don't suceed right away. Some women have trouble finding it--probably something about the difficulty of reaching down there and moving one's fingers with any degree of accuracy...