If i want to learn to play an instrument, say guitar, and just take classes on it (besides school) can I list this as an activity on my application ? It will be just a fun activity, im not trying to join a band or something..
Sure. A couple activities like this that show your personality are great. Obviously they are frosting though, make sure you have the meat and potatoes as well.
There is a category called "hobbies" in the experience section. Anything you've been doing for fun can go there. It may be an ice breaker at an interview, something that the interviewer brings up to help you feel less nervous so don't list something you know almost nothing about because that will make you more nervous rather than less so.