This is a game about sustainable energy use and blowing the crap out of mutant alien zombies.
During the day, you will build up your base and manage your resources in a post-apocalyptic world where oil and natural gas become ever more scarce. Research alternative energy sources and upgrade existing facilities to get enough energy to survive.
Then, during the night, use the energy you produced and conserved during the day to fight off hordes of mutant zombies.
Click with the mouse. Just use the left button, and there should be instructions in game to teach you how to play in campaign mode (click "Play now.").
There's a free-form sandbox mode too.
To build something, click in the menu, and then where you want to build. Make sure you have enough resources first. To repair something, click on it and then hit "R", or select repair from its menu. To disable something, click on it and then hit "disable" from its menu. To upgrade something, click on it and then hit "upgrade" from its menu.
Hold Spacebar to place multiple buildings when in build mode.
Objectives will be given for each level, they are shown in the big blue box when you are not in any sub-menus. Click here to show the last objective again.
Click "Help" to look through all the in game hints and tutorials.