Why no f pawn?

It can expose the king and open the king up for attack.  Here is an example of moving the f-pawn in the opening in a poor circumstance:

f6 at also takes away the most natural development square for the Knight. There are openings where f6 or f5 are perfectly reasonable, but you should absolutely know what you are doing. In the simple openings that are advisable for beginners (and intermediate players), moving the f pawn early is generally just bad.

Let's see a few examples:

These are some drastic examples. There are many more where a beginner can lose a game because of f pawn push. Pushing the f pawn early might not be a mistake by itself, but it has to be played carefully. Beginners will often find themselves in trouble after the f pawn push.

Lasker even formulated stronger: play only your d- and e-pawns.

It is okay to play your f-pawn if you can secure a win. The better moves are the e and d pawn to lockdown the center squares.

I agree there are a few openings I like that use f pawn but who knows I just got into chess and have a lot to learn so 

Does this mean...

in all your games, all the other pawns remain on the second rank all the time?

It's just weakens your king very badly, inviting some of the quickest and easiest mates in chess. Especially as black. There are some informative examples posted above. I move it mid-way through one opening I use if, and only if, the opponent follows a particular move sequence where the block in their own pieces in. Otherwise you're basically pulling down your own pants.

That's nice