Very important principle of chess. The center is the key focus of all openings either directly in the form of seizing it or indirectly by applying pressure on it. Once held, a player can convert it into a flexible attack where we can either attack the kingside, queenside or center of the board. A player who controls the center can often apply enough pressure to achieve these positions where the opponent has very few options because they have so many areas of the board to defend at once.
Pawns in the center is the classical idea of controlling the center. Without the right fortification, pawns in the center are targets. This is the idea behind fiachettos and the Sicilian defenses. But if allowed, a strong pawn center results in a massive space advantage and lead in development through tempo gaining pushes. With a large pawn center, first you need to defend it. Then you can aim to control squares in front of the pawns to prepare breaks. For example, knights in the center can defend the d-pawn and prepare an e-pawn break.
When you have a pawn center advantage, the best way to convert it is to push the pawns further, which is only possible if you can gain a lead in development and properly control the squares in the center. Otherwise you can almost always at least convert it to a lead in space through pushing minor pieces.
if you're defending against a large pawn center with no space (and especially if their king is in the middle still as a result) do anything including pawn sacrifices to break it open!