Clicker, IdlerMouse over aliens to kill them and gain resources/xp. With each successive kill, your resouces/xp per kill rises, giving an incentive to manuall kill aliens. Resources can be spent on purchasing military units to automatically kill aliens for you. Once enough xp has been gained, the player levels up and is rewarded with research points. These can be spent on upgrades to improve the resources per second that military units provide amongst other things.
