Energy is the primary resource for most equip-able items in Starbound. Many Items required affect the energy stat. Armor can be used to increase the energy stat while some weapons and tools use the energy stat. Ranged weapons, such as guns and bows, use energy to fire a shot.
Additionally, Vehicles run primarily on energy. Their health bar is effectively the amount of energy they have. When abilities are used or damage is taken, their energy begins to deplete.