You are fighting against the advancing stickmen from their red house. You are opposed by samurai, barbarians, and others. The difficulty level increases with every second, but your strength also grows, because new stickmen for your army are opening up to you.
You need to click on the pictures with stickmen from below to call them. Each stickman is worth a certain number of coins, which you can get over time or knock out in battle with stickmen.