You can use the word "fun" as a noun or as an adjective when an activity is enjoyable, or you have a good time. This is a very popular word, but sometimes it's irregular, so it's important to understand how to use it correctly.
In these sentences, "fun" is an adjective:
That was fun.
The party we went to last night was fun.
This is fun.
This is the most fun I've had in a long time.
The rides at that amusement park are so much fun.
We had more fun going on the roller coaster than on the tilt-o-whirl.
Notice that the comparative and superlative forms for this adjective don't use "er" or "est." Instead, use "more" and "most" only. The use of "funner" or "funnest" is considered bad grammar. (However, that doesn't stop Americans from using these words incorrectly.)
In these sentences and questions, "fun" is a noun:
Do you want to have some fun?
We had so much fun last night.
What do you like to do for fun?
I like to grow things in my garden. I do it for fun.
You're going to have fun if you go to Florida on vacation.
As you can see from the examples above, the verb "have" is often used with the noun, "fun."
You'll often hear "fun" used in everyday English.
How fun! (An activity sounds or looks fun.)
That looks fun.
Bye. Have fun. (Bye.)
This is not fun. (This is difficult.)
This is so fun. (Listen carefully. This is an example of sarcasm. When said this way, something is not fun.)
She's making fun of you. (make fun = laugh at or criticize)
These people look like they are having fun:
Note: The word "funny" is not exactly the same as the word "fun." If something is funny, it probably makes you laugh or provides amusement. If something is fun, you may or may not be laughing. I have fun while I work on my website, but I'm not laughing while I do it--not usually.