use the mouse (i-game tutorial)

Merge Cannon: Chicken Defense - This game is a mix of two genres of merge and defense!
The army of chickens is marching up to your castle. We need your help now! Merge cannons, upgrade your castle, and defend it from the chickens!
There are waves of chickens that will finish with the end boss chicken! The time has come to merge your cannons and defend your castle from these violent chickens.
Are you ready, or will you chicken out?