IF SOMETHING IS FUN, THEN IT IS SOMETHING THAT YOU ENJOY DOING.
IF SOMETHING IS FUNNY, THEN IT IS SOMETHING THAT MAKES YOU LAUGH.
Halloween is fun or funny. HALLOWEEN WOULD BE CONSIDERED SCARY SO IT CANNOT BE FUNNY. THEREFORE HALLOWEEN WOULD BE CONSIDERED FUN. SOMETHING YOU ENJOY.
That is fun or funny. THAT LOOKS LIKE FUN (EXP: IF YOU SEE SOMEBODY DANCING OR PLAYING A SPORT AND IT LOOKS LIKE YOU WOULD HAVE FUN DOING IT) OR THAT'S FUNNY (EXP: IF YOUR FRIEND SAYS A JOKE YOU COULD SAY "THAT'S FUNNY" OR IF YOU SEE SOMEBODY DOING SOMETHING SILLY YOU CAN SAY "THAT'S FUNNY").
He is fun or funny. HE'S A FUN GUY (YOU ENJOY SPENDING TIME WITH HIM BECAUSE HE MAKES YOU HAVE FUN) HE'S SO FUNNY (HE MAKES YOU LAUGH WITH MANY JOKES, A COMEDIAN)
That movie is fun of funny. THAT MOVIE IS FUNNY. (BECAUSE IT MAKES YOU LAUGH)
HOPE THIS HELPS!