For energy to walk through all the lands, summoning sprites, you must eat fungi, which (seemingly) randomly appear on the ground as pixelated, reddish rectangles. Tap ONCE and a circle appears around it and the Traveler walks over to the spot, picks it up and eats it. You do not eat it or get any benefits from it at the point you PICK IT UP. It's in your back pack for later. Open your back pack and select a mushroom to actually eat it and regain your health.