The epididymides are swellings at the back and top of the testis. They provide for storage, transmission and maturation of sperm.
After sperm are manufactured in the testes they move to the epididymides: highly coiled tubes which are 13 to16 feet long. Here they mature and gain their mobility. 
The epididymides are located within the scrotum, at the back and top of the testis, like a Mohawk haircut.
The easiest way to feel them is after a hot bath or shower, when your scrotal skin is relaxed. Sometimes guys are alerted when they feel these swellings, afraid it’s cancer. However, they are a normal part of the male anatomy.