Locating the bc muscle
I guess it doesn't really matter what you call the muscle you contract when doing Dr. Kegel's exercise, as long as you do it correctly and consistently. However, being a stickler for accuracy, I have to point out that men contract a different muscle than women when doing Kegels and it isn't the PC (pubococcygeus). It's actually the BC (bulbocavernosus). This is probably the only place on the Internet where you'll find this distinction. Most will probably find it easier to "go with the flow" and conform to years of misconception by just calling it the PC.
Why isn't it the same muscle? Men and women are different. Females have essentially internal sex organs, males essentially external. The PC muscle is located in such a way that it is above and behind the penis and it contracts up into the pelvis. While its action on the rectum may add a little to the pull on the penis, it isn't the main muscle being exercised when men do Kegels. Of course men can contract their PC muscle. They do it every time they have a bowel movement. Some probably contract it while doing the Kegel exercise (by involving the anal area), but it isn't necessary to do so for a stronger penis.
First part of the anatomy lesson. Please see the "Pelvic Muscles" illustration below. The PC muscle, along with the Iliococcygeus muscle (IC) make up the Levator ani muscle which serves as the "floor" of the pelvis, keeping your abdominal contents from sliding into your perineum. It also plays a roll in bowel movements. Both the PC and IC are made of two flat sheets of muscle (one on each side). The PC is attached in the front to the pubic bone. The two halves sweep along the sides of the pelvis and attach at the rear to the coccyx (tail bone). The IC attaches to the pelvic bone on the sides and at the coccyx in the rear like the PC. In a side view (not shown) the Levator ani is funnel-shaped, surrounding the rectum/anus. One of its main purposes is to pull the rectum back up into position after a bowel movement.
Note how the PC forms a "U" shape as it wraps around the rectum. The urethra and vagina in women are much more in contact with the PC than the urethra is in men. In addition to forming a sling around the rectum, the PC passes by the sides of and inserts into the vagina and urethra in women. The contractions of the muscle can be felt by a finger in the vagina. This is why Dr. Kegel advised his female patients (he was a gynecologist) to exercise the PC muscle. It helps tighten the vaginal canal, rectum, and urethra especially after childbirth which can stretch these pelvic structures and cause urinary incontinence and uterine prolapse. Dr. Kegel showed that exercising the PC muscle could strengthen the female perineum and help cure the physical ailments as well as improve their sex lives.*
Where is the bulbocavernosus (BC) muscle? Please see the "Perineal Muscles" illustration below for the second part of the anatomy lesson. Both sexes have a pair of BC muscles. In females it surrounds the vaginal opening. Some women can independently contract the BC and the PC. Most contract both at the same time. In the male, the two halves of the BC are joined in a "herringbone" pattern surrounding the bulb of the penis (the internal base of the corpus spongiosum).
The BC muscle has two main purposes. One is to force liquid (urine or semen) out of the urethra. It does this by way of the herringbone interlacing of muscle fibers which, as they contract, milk the urethra toward the meatus (opening at the tip of the glans). It also happens to cause the penis to be pulled into the body (the LOT tug-back). This happens every time a man urinates. It also happens with much greater force, and with rhythmic contractions, when he ejaculates. The BC muscle is the main ejector of semen. This is why ejaculation improves by exercising it.
The other function of the BC is to squeeze blood into the corpus spongiosum and the glans. The bulb of the penis is a reservoir of blood. At the time of greatest arousal voluntary or reflex contractions of the BC and Ischiocavernosus muscles force blood into the corpora. The Ischiocavernosus muscles surround the crura of the penis (legs of the corpora cavernosa). With both sets of muscles contracting on the base and legs of the penis, a maximum erection is achieved.
Locating the BC: The adage about stopping the flow of urine is valid in locating the BC muscle in men. Even though the urethra does have a sphincter (just below the prostate) to stop urine flow, contraction of the BC will "milk" the urethra and let the man know which muscle to use for Kegel's exercise. The BC muscle can also be felt with the fingers by placing them between the scrotum and the anus. Contractions felt through the skin at this point (in the midline) are from the BC muscle. The illustration "P.C. or B.C." below shows the relationship of the PC muscle in men as it passes by the prostate and surrounds the rectum (top two images). It also shows the location of the BC muscle at the base of the penis (two lower images).
Searching the Internet for instructions on how men should do Kegels will bring a wide variety of exercise plans. Some say start with 20 at a sitting, twice a day, and work up to 100 doing them daily for six weeks. Another site suggests working up to 300 per day, holding each contraction for a few seconds, and doing that many every day "for the rest of your life." There's no set answer. Each man must evaluate his situation and exercise accordingly. The plan that starts out gradually, with a few quick squeezes, and work up to a hundred holding each one for a few seconds, sounds like a good one to start with. A few days a week should be enough to evaluate your situation. If you don't notice a change in the force of your ejaculations or the strength of your erections, then more exercise of the BC, not PC, might be in order.
*Here is Kegel's original article for those interested.