Star's energy is like a battery in your cell-phone. A star needs energy to do any activities in game. If the energy level hits 0, the star will pass out. The energy recovers by time. Even when you are off the game, the energy will recover at the speed of 1 by 30 seconds. You may purchase Recovery Ring to double the speed. If you need an instant boost of the energy, buy Energy Drink. Both Recovery Ring and Energy Drink are sold in Star's Profile page.
You can always check the star’s energy level here.
You can buy Energy Drink by clicking on the Energy button. It’ll instantly boost your star’s energy to maximum.
Click on the ring icon to buy Recovery Ring. It’ll double the speed of energy recovery of the star. Once you purchase the Ring, the button will be shown with colors.
You can get bonus energy if you play during the meal times. There are 4 meal times a day and it’ll give you a chance to give bonus energy to the star.