Tears are produced by tear glands, which are small glands inside your upper eyelid. Tears keep the surface of your eyeball clean and moist, and help protect your eye from damage.
When you blink, your eyelids spread the tears over the surface of the eye. Sometimes tears flow over your lower eyelid, but mostly the tears flow down a tiny tube at the edge of your lower eyelid, next to your nose – if you look very carefully you can see a tiny dot that is the beginning of this tube. This tube carries the tears to the back of your nose (and this is why your nose ‘runs’ when you cry!)
