The endgame

The endgame has its own laws. There are only a few pieces left on the board. The king turns into an active piece., because the danger from mating attacks is less. It supports its own pawns and attacks the opposing ones. The focus is now on the struggle to promote pawns.
In the endgame the king becomes a strong piece. It supports its own pawns and attacks those of the opponent. It soon comes about that the two kings are opposite each other and holding each other in check. That is called the opposition and is quite an important tactic in the endgame.
This ending is the way things usually finish: a pawn promotes to queen, all other material has left the board. Now you need to know how to mate with the queen alone.
The stage before mating with the queen: White manages to promote his pawn. That always works when White gets control of the queening square.
Not every ending with king and pawn against king is a win. If the defending side can hold the queening square it has the best chances of a draw. This defensive technique has as its focus the opposition.
If in the endgame pawns are running free every centimetre will count. There is a simple trick for working out whether a defending king can catch a sprinting passed pawn.
Checkmating with two rooks is not difficult. The king is not needed. As soon as you understand how the rooks cooperate you have mastered the process.
Mate can be delivered even with a single rook and no other piece. It is however more demanding than mate with the queen alone. The king must help actively. And which manoeuvre is required? Of course, the opposition.

In the endgame the king becomes strong. It helps its pawns on their way to becoming queens or wins the opponent's pawns. In many technical mates it has to help its pieces.