At the beginning of your adventure in Harry Potter: Hogwarts Mystery, your character has only 15 energy points at his disposal. The energy is used to take part in events which can be completed faster by utilizing completing the right interactions. The interactions spend your energy points (from 1 to 4 in the initial stages of the gameplay). Spent energy points return in form of event points.
Your energy bar is increased with each new experience level. Each level gives you an additional energy point. This system may seem to be slow, but the experience levels in Harry Potter: Hogwarts Mystery are attained quickly, as you receive a few hundred experience points for each event. Moreover, the game replenishes your energy bar with each attained level. New experience levels also reward you with diamonds and unlock new content such as clothes or chambers.