Fun is used to describe something that you enjoy doing.
It is fun to play football / I have fun when I learn English
Funny: funny is normally used to talk about things that make you laugh
This movie is very funny. I haven't stopped laughing / I always laugh at funny jokes
Try remember:
I really like to watch football. I have fun watching football. I enjoy watching football. I don't normally laugh watching football. Football isn't normally funny.