Your farm has come under attack from the most unnatural collection of enemies possible: wolves, ritualistic cultists and the United States's military. It's not obvious what exactly has prompted such a conflict, but all of your enemies seem to be after the same thing: your livestock - or more specifically your sheep.
Keys 1,2,3,4 can be used to switch between weapons quickly.
Use the mouse to shoot your enemies.
Research upgrades and new technology by clicking on the research tier buttons.