Yeah, the doc just presses against the top of your scrotum and have you turn your head an cough a few times, and the doc will do this for both sides of your scrotum. This is to test for hernia (large intestine slipping out your abdomen into your scrotum). Then the doc will gently rub each testicle, checking for lumps (testicular cancer), or any other problems with your balls. Then the doc may or may not just quickly lift up your penis to check underneath it, and if you're uncut, he/she may just retract the foreskin real quick just to see if it can retract OK, and there's no infection underneath. These last things of checking the penis are kind of optional - some docs do it, some don't. But you can count on the hernia and ball check.
It takes like 10 seconds tops - its over before you know it. You probably won't even have time to get an erection. If you do, its nothing to be embarrassed about - the doc has seen that happen MANY times before.