A knock-away is type of fake. It is used to either knocks-away an opponent's guard to create an opening for you to attack or it is a counterattack you use after your attack has been knocked-away by an opponent.
Perform a knock-away. Start your attack as you normally would, except, instead of attacking, use the attack to knock down the opponent's guard to create an opening, and then attack the opening. You may also use both hands to knock down the opponent's guard, similar to climbing motion, and then attack over the guard. You may also attack under the guard after it is knocked down. For example, use the leading arm to knock down the opponent's guard, and, just as the opponent is bringing the guard back up, perform a side thrust kick under the guard.
Perform a counterattack after a knock-away. Perform an attack, such as a jab, slightly slower than usual so the opponent is able to block it and knock it away. Then, instead of retracting the jab, snap it into another attack. The entire motion of the technique is planned, the jab is not intended to connect, but it should appear as such to the opponent.