Strategy & opening play
Centre
The central squares are d4, e4, d5 and e5. Controlling them often helps pieces switch between the two wings. Control can come from occupying squares with pawns or attacking them with pieces; a large pawn centre is not automatically stable.
A practical example
White pawns on d4 and e4 claim space. Black can pressure them with pieces and later challenge them with c5 or e5. The important question is whether White can maintain, advance or exchange the centre favourably.
A common mistake
Advancing every central pawn. A push gives up control of some squares and may weaken the pawn chain or king safety. Even an apparently free central pawn may be tactically poisoned.
Try this in your next review
Count attackers and defenders of the four central squares. Then find a suitable pawn break and calculate which lines open after an exchange.