Deflection forces the opponent piece to leave its position in order to attack the piece protected by the deflected piece.
You deflect a piece .
This piece is forced to move.
Now the other piece which is defended by the deflected piece is vulnerable.
You can capture it.
Let's see an example.
diagram 1
Rook attacks Queen . After any move of the Queen , Knight will capture the Bishop.
If Bishop captures the Rook , Knight wiill fork The King and the Queen. See diagram 2
Diagram 2
More examples: Watch our deflection video - other examples