The objective of each player is to place the opponent’s king ‘under attack’ in such a way that the opponent has no legal move.
The player who achieves this goal is said to have ‘checkmated’ the opponent’s king and to have won the game.
Leaving one’s own king under attack, exposing one’s own king to attack and also ’capturing’ the opponent’s king are not allowed. The opponent whose king has been checkmated has lost the game.