If you have ran out of energy please tap the plus sign next to your energy level icon in the upper left-hand corner of the screen. You will be offered to watch an ad to get +5 points of energy.
After you watch all the available commercials you will be able to ask your neighbours for energy. You just need to tap "Ask" and the list of your neighbours will be displayed. Choose the neighbours you would like to ask energy from and tap "Ask" again. To ask all neighbours for energy, tick "Select all" at the bottom left. Your neighbours will get a request to send you +3 points of energy.