You don't want to move it in lieu of a developing move, especially when you weaken your king position. There is a time to move it....Start out not moving it. learn those ideas later.
The f pawn

Moving the f-pawn weakens the kingside pawn structure. Since it's logical and in most openings you want to castle kingside, it's not a good idea to move the f-pawn.
If you can win material, or think that your activity (if you got a rook on f1 it will get active behind the pawn) compensate for the weakned pawn structure. But in the opening after 1: f4!?, white has not developed his white-squared bishop (as he has efter 1: e4!) and will often find himself in a worse position.

The problem isn't a move such as 1. f4!?. Rather, most beginner players are told to not move the f pawn so that they avoid plans such as f3 g4 or f3 e4 while under developed and uncastled, which I commonly see when facing lower rated players. This kind of weakening with no real purpose usually makes for an easy win.

example of when it is bad to move your f pawn:
black is underdeveloped, and exposes his king to an annoying check allowing for this common tactic. also sometimes the other diagonal can become exposed, for example if black plays f6, and white has a bishop on c4, black will no longer be able to castle kingside as the bishop would then be controlling the square black would castle into.
example of when it is good to move the f pawn:
So I have been told never to move my f pawn, but I see all kinds of masters that do. Was what I was told wrong or what?