blocking and pinning are very useful tactics in playing ziangqi(chinese chess). the rook is the most important piece, like a queen in chess, you must put your rook in action at the opening, so blocking your opponent's rook is a way to get the initiative, the most common way is rook+cannon to block your opponent's rook. on the other hand, if you rook is unprotected, your rook is pinned by your opponent.
there are many way for blocking and pinning depends on the situation.