There are waves of red stickmen coming in each level, and you need to set up defenses and blue stickmen to fight the red ones until their wave is over so you can move on to the next level. As the waves go by, you win coins that you can spend on better defenses. Each wave is stronger than the last. You can buy the weapons in the main menu's shop. After clicking on a unit, you can choose where to put it on the streets. Have fun and good luck!