Your aim is to collect wood during the day and build up your defenses. You can give commands to each of the beavers separately, so one of them can cut trees to get wood, while the other builds barricades so the wolves can't attack them.
The gameplay is relatively similar to a tower defense, since you have to hold your position while you build your defenses. And if you build one defensive barrier on top of another one, you can upgrade it so it becomes more resistant to enemy attack.
Twigs is a really nice strategy game with really fun graphics. The whole idea of the game is so crazy that you'll find yourself smiling at the sight of your two beavers trying not to be devoured by wolves.