How to Have Fun in Spanish -- Really!
First of all, as the little introduction above tells my readers, you do not use tener divertido in Spanish when you want to say to have fun. Beyond there being a verb that answers nicely to the English expression, there are a few other things that you need to observe in order to cover a range of related expressions about having a good time.
The verb for expressing to have fun is divertirse. It is irregular (a stem-changing verb) and reflexive:
The singular forms, first- through third person are:
me divierto: I have or am having fun
te diviertes: You have or are having fun
se divierte: He, she or you formal: has fun or is having fun (or, if the subject is you, have or are having fun)
The plural forms, first- through third person are:
nos divertimos: We have or are having fun
os divertís: You have or are having fun
se divierten: They have or are having fun
Another related verb (plus preposition), meaning to enjoy is gozar de. The preposition de is followed by a noun that refers to the thing enjoyed:
Juan goza de su familia (Juan enjoys his family).
Gozamos de las fiestas patrias (We enjoy national holidays).
Similar to the previous verb is disfrutar -- also followed by de:
Ella siempre ha disfrutado de buena salud (She has always enjoyed good health).
Yo disfruto de mi buena fortuna (I enjoy my good fortune).
Finally, no discussion of fun and enjoyment would be complete without a reminder about the verb gustar. It is always used with an indirect object showing the person or persons who are pleased. It is not an equivalent of the verb to like. Note that a clarifying phrase can be used to indicate to whom le (or les) refers.
Me gustan las fiestas (literally, Parties please me). The grammatical subject is fiestas.
A Juan le gusta navegar en barco de vela (literally, To sail pleases Juan). The grammatical subject is navegar.