A Kegel is a type of pelvic floor contraction, first described in Western medical literature by Dr. Arnold Kegel in 1948. Contracting the muscles of the pelvic floor (one's bottom) strengthen and tone them and can have beneficial effects for many women experiencing stress incontinence. (Other types of incontinence don't respond so well to these exercises alone.)
To find these muscles and to learn to perform a Kegel, stop the flow of urine while urinating and then allow the flow again. If you are successful, you just did a Kegel; you've located the muscles that you want to work with and you've executed the movement that you want them to do—contract and release. It's okay to do this several times in order to embody your learning.
However, the exercise itself should *not* be done while urinating. Doing the exercise this way runs the risk of creating a detrusor (bladder muscle) dyscoordination and more incontinence or leaking. And Kegels are most useful if done standing as this is the position in which most women experience incontinence or leaking. Try doing pelvic floor contractions in various positions—lunge to each side, lunge forward, bend in plies. This will enhance neuro-muscular coordination between the large muscles of the thighs and buttocks with the muscles of the pelvic floor.
It's recommended to hold pelvic floor contractions for 10 seconds. This is an arbitrary number that will likely cover the amount of time it takes for a bout of laughing, coughing or sneezing.
To engage the more difficult eccentric movement of the pelvic floor muscles, don't just let go when done with holding a contraction. Slowly and deliberately lower the intensity of the contraction, releasing with control. This is much more difficult than the concentric movement of contracting the muscles and it will garner you much greater reward.