The Cell Stage is just one of many evolution stages. This is simplest form of creatures you will play. The goal in the 2D water environment the creature will find itself in is to eat smaller creatures and/or algae and earn points towards new body parts. The choices you made now will impact your creature throughout the whole game. After enough time of swimming around eating, you'll earn enough points for the body parts and the ability to live on land. This is the start of the next stage - the Creature Phase.
[Source: EA Games Press Release]