when people cry, why do tears come out?

The tear ducts in your eyes produce the tears, and some are probably produced when the person is squeezing their eyes shut while crying. So that's the HOW.
The why? Well, I just did some research, and it appears that tears are produced because of the strong emotions. Studies have shown that people actually feel better after crying, and also that tears contain stress hormones, so some scientists have a theory that we produce tears to get rid of that stress.