Becoming comfortable with doing a self exam is a good idea for guys, as testicular cancer is common among men form mid teens to mid 40's.
Detailed steps form VideoJug:
How To Do A Testicular Self-Exam
We show how to conduct a testicular self-examination. A video for men to raise awareness about cancer.
You Will Need
* 1 mirror
Examine yourself using a mirror
Using a mirror, examine the scrotum, looking for any lumps on the skin or swellings inside.
Feel for differences between the testicles
Cradle the whole scrotum and testicles in the palm of your hand and feel for any differences between the testicles. One is usually larger and lying lower and this is completely normal.
Check for lumps and swellings
Use both hands and gently roll each testicle between thumb and forefinger, checking for any lumps or swellings. Be aware of heaviness or hardness in part or all of the testicle. Your testicles should be smooth to touch except for the epididymis, which is a soft ‘sausage’ like tube that lies at the top and back of the testicles and carries sperm to the penis.