The creature stage is sort of like the cell stage, except you can be friends with other creatures or kill them.  When you start off the creature stage, you need to find other creatures that live on your planet.  You can also find rare items, like new body parts.  When you meet another creature, you can choose to either be friends with it or to kill them.  To be friends with them, you will need special body parts to do things like dance, pose, sing, or charm.   To fight, you will need weapons on your creature, like poison spitters, horns, claws, or spiked teeth.  After you have made enough friends, or killed enough enemies, you will move on to the tribal stage.