In Deeeep.io, start with one of four available ones in Tier 1 including Fish, Blobfish, Worm, or Piranha and then move around to look for food. That this is the first important goal to help you fulfill your own XP bar (at the bottom of the screen). Whenever it is full, the animal will evolve to another one. With a total of 10 Tiers , you need to overcome each to attain the highest evolvement. Have fun.