Before Discovered Attack
Bishop is between the Rook and the opponent Queen.
After Discovered Attack
After the Bishop moves out of the way of the Rook and checks , the Rook attacks the Queen. This is Discovered attack . Since the King is in check , The Queen cannot escape and the Rook will capture the King.
Before Discovered Check
After the Knight moves out of the way of the Rook ,
After Discovered Check
After the Knight moves out of the way of the Rook , the Rook checks and the Knight threatens the Bishop. No matter what move Black plays, White Knight will capture the Bishop.