A cannon is a block that you can place, then when you pull the lever on it, it launches TNT from the Cannon. Once you launch it, in order to launch another block of TNT, you have to right-click the Cannon with a block of TNT in your hand. It will remove the block of TNT from your inventory and then you can pull the lever again and it launches another block of TNT! It can lauch TNT up to 25 blocks away. A Cannon can be upgraded by placing a two canons next to each other! Creating a large canon, which can fire up to 4 blocks of TNT, up to 35 blocks away!