Play g2-g4 and the square g2 is empty for the rest of the game. Not empty for a few moves: empty for good, because nothing will ever put a pawn back on it. That is what makes pawn moves different from every other move you make.
A pawn on e2 has six moves in it at the outside (e3, e4, e5, e6, e7, e8) and then it is not a pawn any more. Six one-way steps, and each one is spent.
The only piece with no reverse gear
Rooks, bishops, queens and kings retreat as easily as they advance. A knight on d2 can go back to b1 or f1, and four of its eight squares are behind it. The pawn is the sole exception in the whole Laws of Chess, and it cannot capture backwards either: a white pawn on f4 attacks e5 and g5, and an enemy knight that lands on g3 is perfectly safe from it. The complete list of retreating pieces is on which pieces can move backwards.
What it costs you
Here is a position I see constantly in club games, usually after somebody chased a bishop with h3 and g4 and enjoyed it.
7 
4 
g Count what the white king actually has in front of him. The pawn on f2 covers g3. Nothing covers h3, and nothing ever can, because the only pawn that could defend it stood on g2 and is now on g4. A black queen or knight that reaches h3 does so for free. Black’s kingside, by contrast, is untouched: f7, g7 and h7 defend each other and every square in front of the king is covered.
Two pawn moves, no material lost, and one side has a permanent hole. That is why pawn structure is a subject and piece placement mostly is not: you can always bring a knight home.
One question before every pawn move
Before any pawn move, ask one question. Not what does this attack, but what does this stop defending. Doubled pawns, an isolated pawn, a hole on d5: none of those can be undone, and all of them start with one pawn move that looked natural. Endgames are decided by the same thing, which is why pawn endgame puzzles are the ones I set students who keep drawing won positions.
The good news is that the same rule works for you. A pawn you push to the seventh rank cannot be made to go home either, and a pawn on the seventh is nearly a queen.