Examples

White can win with the decoy Bc7!
Black's queen is attacked, and has only two safe squares available, taking on c7, or moving to c5.
In either case the queen is lured to the c-file, where it is facing the rook on c1.
White can win with Bxf7+, with a discovered attack on Black's queen.

The decoy can also be on the piece attacked directly, as in the following example:

Black can win with the decoy Rxc2+!
Kd1 would run into checkmate with Qb1+, therefore White has to accept the decoy with Kxc2.
The king is now lured to c2, where it can be attacked with Bxb3+, with a discovered attack on White's queen.

Related combinations

Trade into discovered attack is similar to decoy into discovered attack, but the first move is a trade instead of a sacrifice. It is also possible to decoy a piece to a square where it can be attacked in a subsequent tactic other than a discovered attack. And you can decoy the king into checkmate.