It's a very common and versatile verb, used in many contexts:
* Divertirse en una fiesta: To have fun at a party.
* Divertirse con los amigos: To have fun with friends.
* Divertirse jugando: To have fun playing.
* Divertirse leyendo un libro: To have fun reading a book.
Keep in mind that "diviertise" is not a word in Spanish. It's the informal imperative form of "divertirse". You would use it in a casual situation, like telling someone to have fun.