The Catapult is a siege weapon acquired early into the game that can launch three different types of ammo at the target's yard. It can fire Twig Missiles, Pebble Bombs, and Putty Rage.
The Twig Missile is an attack using Twigs that deal damage to a concentrated area. It is best to use against Aerial Defense Towers without hitting nearby Storage Silos. It is also effective against Cannon Towers and Tesla Towers. Selecting a larger amount of resources to fling will deal more damage.
The Pebble Bomb is an attack which uses Pebbles, and is acquired by upgrading your Catapult to Level 2. It deals damage over a larger area than the Twig Missile. It is effective against Sniper Towers, Laser Towers, and Monster Bunkers. Selecting a larger amount of resources to fling will result in the range getting slightly bigger(from small option to medium option) and will deal more damage.
The Putty Rage is another attack option using Putty, and is obtained by upgrading your Catapult to Level 3. It differs from the other attack options in that it must be flung on your Monsters. Once flung, monsters affected by the Putty Rage will have increased armor, movement speed, and attack speed. Selecting a larger amount of resources to fling in will give your monsters stronger buff effects, and will make the buff last longer.