In the game you need Fun Points. Fun points wil transfer into energy. More about energy you can read here. In the shop you can buy decorations which gives you a certain amount of fun points. A list with decorations in the game, you can find here.
If you don't have any fun points anymore, you have to buy a decoration in the shop which gives you fun points again. Every decoration has a certain amount of fun points. When do you don't have fun points anymore, and your energy bar is empty, your workers will not work. You can fill up your queue in the buildings, but they start to work again, as soon as you have fun points again.