White has played 1 e2-e4 pushing her pawn forwards two squares. Black's king is in check.

Although Black's king is in the centre of the board, he has no moves because his own pieces get in his way on the 5th and 6th ranks, and White's king controls c4, d4 and e4.

Incredibly, Black is in checkmate! One tiny little pawn proved stronger than all of those monstrous pieces. Of course, this is a made-up position but it does teach us a lesson:

Always keep an eye on your opponent's king to see if there is a checkmate there.