The center of the chess board is the area you should play on the most. Play at the center with all the power. If you do, you can get rewarded of winning the game most of the time.
Why is the Center Important?
It is important for you to put your pieces on the center because it can almost go to any side of the board.
What if the pawns already have the center?
If the pawns already have the center then it is always better to attack in the sides which are also known as wings. It is always good for you to attack the center from the wings if the center is filled with pawns. In the following position I will show you the Nimzo-Indian where black attacks the center from the wings:
If there was a position that was clogged and there are no chances of attacking in any side of the board then it is better to exchange pieces.