Zizka helped develop tactics of using wagon forts, called vozova hradba in Czech or Wagenburg by the Germans, as mobile fortifications. When the Hussite army faced a numerically superior opponent they prepared carts for the battle by forming them into squares or circles. The carts were joined wheel to wheel by chains and positioned aslant, with their corners attached to each other, so that horses could be harnessed to them quickly, if necessary. In front of this wall of carts a ditch was dug by camp followers. The crew of each cart consisted of 16-22 soldiers: 4-8 crossbowmen, 2 handgunners, 6-8 soldiers equipped with pikes or flails (the flail was the Hussite "national weapon"), 2 shield carriers and 2 drivers.  The Hussites' battle consisted of two stages, the first defensive, the second an offensive counterattack. In the first stage the army placed the carts near the enemy army and by means of artillery fire provoked the enemy into battle. The artillery would usually inflict heavy casualties at close range.  In order to avoid more losses, the enemy knights finally attacked. Then the infantry hidden behind the carts used firearms and crossbows to ward off the attack, weakening the enemy. The shooters aimed first at the horses, depriving the cavalry of its main advantage. Many of the knights died as their horses were shot and they fell.  As soon as the enemy's morale was lowered, the second stage, an offensive counterattack, began. The infantry and the cavalry burst out from behind the carts striking violently at the enemy, mostly from the flanks. While fighting on the flanks and being shelled from the carts the enemy was not able to put up much resistance. They were forced to withdraw, leaving behind dismounted knights in heavy armor who were unable to escape the battlefield. The enemy armies suffered heavy losses and the Hussites soon had the reputation of not taking captives.

Answer this question "How did Zizka use wagon forts?" by extracting the answer from the text above.
they prepared carts for the battle by forming them into squares or circles.