a pc muscle are the muscles inside the vagina, it just gives guys a tighter feel, some guys like that some dont,because its tighter for him the friction can cause him to cum faster.. hope that helped.

Yeah what guy wants to cum fast? I sure dont its embarassing. However to give some insight on this if you are looking to strenthen your pubbococcygeus,( or PC muscle ) Which is a good thing to do because it will increase the intensity of your orgasms period. The PC muscle should be about 3/4 inches wide when fully developed. It's located about 2 inches within the vagina and runs circularly. This muscle contains most of the nerve endings found in the vagina and is the source of the sexual vagina feeling. First you need to find the muscle. Sit on the toilet, spread your legs as far as possible, and start and stop the flow of urine. For both women and men, the PC muscle is the only one that can accomplish this. Start and stop the flow three times to set the PC action in your mind. Then empty the bladder completely. To make sure of working the right muscle while exercising, women can insert a finger into the vagina and feel the contractions. Exercise 1 (Squeeze): Squeeze and hold the PC muscle for about three seconds .. relax .. and repeat the process. This exercise may be repeated as often during the day as desired. Short sets of 25 are recommended. If you become sore, it's important to stop exercising your PC muscle for a few days. Exercise 2 (Tighten): Contract and release the PC muscle about ten contractions at a time, depending on the condition of the muscle. The contractions during orgasms are more rapid. Exercise 3 (Holds): Maximally contract the PC and hold for 10 seconds. At the very end of the contraction, squeeze once rapidly, harder and deeper, then release for 10 seconds. GOOD LUCK!

You are referring to the pubococcygeal muscles. These are you pelvic floor muscles. To exercise them squeeze like you are stopping the flow of urine, mid-stream, and hold for 10-15 seconds.