The anterior fornix - sometimes known as the A-spot, AFE zone, or "deep spot" - was first noted by Dr. Chua Chee Ann, a Malaysian scientist. He now runs the website Aspot-Pioneer.com to disperse his findings.
In 1993, Dr. Chua noticed that stimulating a certain spot deep inside the vagina - on the same wall as the G-spot, but up farther toward the cervix - would cause his female subjects to quickly become aroused and begin to lubricate. This led him to the discovery and belief that the A-spot is not only a remarkable erogenous zone, but also may be the key to unleashing natural lubrication in cases where the woman doesn't get as wet as she'd like to. Dr. Chua now markets his findings toward couples who fear that the woman is "frigid" because she doesn't get wet or rarely gets aroused.
You may be wondering: what's the best way to stimulate this zone? Does it need to be romanced first, like the clitoris? Does it need time to swell up and become sensitive, like the G-spot? Sources say no. Dr. Chua found that regular stimulation of the A-spot, even with no foreplay involved, induced arousal and wetness in female subjects. Some women were even able to achieve intense orgasms from this kind of stimulation alone. It seems strange to think that part of your "foreplay" might involve being deeply penetrated, but it seems to work well for many women!
You can find the A-spot by locating your cervix (the opening to the womb, at the very deepest part of the vagina) and then moving your fingers forward, toward your belly, into the tiny "dip" or "valley" just in front of the cervix. That's the anterior fornix (there's also a posterior one, which is, of course, behind the cervix). If stimulating it feels strange at first, don't worry; touching your clit and/or G-spot probably felt weird at one point, too. It's all about learning to perceive that new sensation as pleasure, which shouldn't take long.
As with any unfamiliar erogenous zone, it may be helpful to add clitoral stimulation while touching the A-spot. This will teach your body to associate that spot with good feelings even moreso than it already would.
Dr. Chua recommends a "scooping motion." Imagine the commonly-recommended firm "come hither" motion that you would use on your G-spot, but make it a little broader and longer so you cover the whole AFE zone.
If your fingers are too short to reach your A-spot, have a partner give it a try with their fingers or penis - seek out positions that allow the penis to stroke your front wall and get up into that fornix, such as doggie-style. The thrusts may need to be deeper and smaller than you're used to, for maximum pleasure potential. It's also possible to access the A-spot using a dildo, ideally one with an upward curve and enough length to reach the deepest part of your vagina (generally about 5 or 6 inches).
You may notice that you're producing a lot more wetness than usual, or you might just notice a strange new kind of pleasure. Whatever the result, enjoy playing with your new discovery!