Discovered attacks are among the most powerful tactical devices in chess because they create two simultaneous threats. When a piece moves, it uncovers an attack from a bishop, rook, or queen behind it. If the moving piece also delivers a threat (especially check), the opponent must deal with the immediate threat while also facing the uncovered attack.
The most dangerous form of discovered attack is the discovered check, where the uncovered piece gives check to the king. Since the opponent must escape check immediately, the moving piece can capture virtually anything on the board or relocate to an ideal square with complete impunity.
To create discovered attack opportunities, position your pieces so that a bishop, rook, or queen is aimed at an enemy target with one of your own pieces on the line. Then look for powerful squares where the front piece can move to, ideally creating a fork, a threat to capture material, or a check of its own.