Enemies will traverse an indicated path, surrounded by a grid. Place turrets inside the grid to kill enemies before they reach the end. Be mindful of how much money you have, the type of turret you use, where you place your turrets and if you chose to upgrade or sell them. Killing enemies gives you money to buy/upgrade the turrets.
Click on the frame then move in the direction you want to go to move the game view inside the frame. Click on the turrets then on the grid where you want them to place the turret. Click on a turret to upgrade or sell it for the indicated price. Features inclide a menu with the option to play or quit which sends you to the loading screen. You can also choose which level you want to do if you have completed level one and the level before the one you want to play. Money is shown next to the turrets you can use.
Replay button doesn't work: you have to restart all over again if you ever fail or want to retry a level.