How to say 'fun' in Spanish: Divertido. Let's try that. Or you could say 'divertida', if you're talking about something in the feminine. Divertido or divertida.
If you want to say something like 'the party was fun', you could say, "La fiesta estuvo divertida." Let's try that. If you want to say 'the game was fun', you would say, "El partido estuvo divertido." Let's try that. Repeat after me: El partido estuvo divertido; the game was fun.
In the first example, we 'divertida' because we were talking about a party. In this example, we used 'divertido' because we were talking about a game. Divertido or divertida; they both mean 'fun' in Spanish.