Each hero has six equipment slots. Some of them can be filled with crafted equipment. To do this, find their base pieces. Tap on an equipment slot to view where you can find its base piece. After you have all six equipment slots filled on a single hero, you can fuse the equipment with the hero to promote them. Promotion gives that hero a boost to stats and will unlock new abilities. Use the Blitz option to complete levels quickly and farm for equipment.