You begin the game as a tiny amoeba-like creature that arrived on the planet via meteor. If you are a carnivore, you must eat little red protein chunks. If you are a herbivore, you must nibble on green vegetation. Either way the game play is similar: swim around eating and growing while avoiding being eaten by bigger spores that are also eating and growing.
You earn "DNA points" which you can occasionally use to add body parts, weapons, jets, and other utilities to your little spore. You must earn these new parts by finding them in glowing chunks of meteor rock, by gobbling up other spores, or finding them as you swim about. You can add multiple mouths, tons of eyes, flagella, a poisonous spray, and deadly spikes to whatever end your imagination desires. Covering your spore with spikes pointing every direction provides both offensive and defensive benefits. Most additions have some kind of benefit to your spore, but others are simply cosmetic.
This stage of the game is very unique and really cannot be classified in any standard PC game genre. It is also quite brief. There is even a badge for completing it in under 8 minutes. While quick and simple, this stage definitely sets the mood and provides context for the enventual galactic scope of the game. When you are exploring space later on in your creature's life, reflecting back on its time as a tiny little protein eating spore will add to the sense of accomplishment.