Apply a small amount of your favorite lubricant to your erect penis and to the insides of your upper thighs. Don't use too much; you can always apply more lube later if you need it. Get into a sitting position with your knees bent toward your chest, and the soles of your feet flat on whatever surface you're sitting on. Your back should be resting firmly against something. (For example, you can sit on a sofa with your back against an arm, or sit on the floor with your back against a wall.) You may want to put a towel under you to avoid having to clean up a mess afterward. Firmly clamp your erect penis between your lubricated thighs and start a slow rocking or thrusting motion with your hips. If you've got the right amount of lubricant and you develop the right thrusting motion, your erect penis will slide in and out between your thighs and will feel like it does when it's inside a woman's vagina. If you squeeze your thighs together very tightly, you can tighten the grip on your penis and create more friction, the way a woman's vagina does when she tightens her pelvic muscles.
The next time you take a bath (not a shower), Sit up straight in the tub so the lower half of your body, including your "special" area, is submerged. Make sure your legs are straight and together. Put your penis between your thighs (your penis may not be flexible enough to do this), and start pumping in between your thighs. The feeling of penetration and the warm, slippery water feels unbelievable.