Instructions
See whether there's any place a king can move without being captured. Remember that kings can move only to one spot in any direction; forward, backward, to the right, to the left, forward left diagonal, forward right diagonal, backward right diagonal and backward left diagonal.
Check to see if there's any piece that can be moved in the line of the king in order to save the king from checkmate. If you can move another piece like a bishop or queen in front of your king to keep your king from being captured, then no checkmate is made.
Determine whether you can capture one of your opponent's pieces that is threatening your king. If you can capture the piece that is threatening your king, you can take that piece out of the game and eliminate the checkmate.
Determine whether your king can capture one of your opponent's pieces, thus eliminating the checkmate. If your king can take out the opponent's piece that is threatening the checkmate, your opponent does not have a checkmate.
Call it a checkmate if the king cannot take out the piece threatening it, if no piece can take out the piece threatening the king, if the king cannot move in any direction to avoid the checkmate and if there's no piece that can be moved in the way of a king's capture in order to avoid the checkmate.