Creature Phase
The creature phase is where the game really begins to kick off. Your creature has now moved into a 3D world and the whole planet is open for you to explore, though you will most probably stick to one small area for the time. The goal of the creature stage is to evolve your creature to a level where its brain development is sufficiently high enough that it becomes mostly sentient.
Similarly to the cell phase, this is done by gaining DNA points through finding or hunting for food. As DNA points are collected, the creature will gain the ability to mate with another of its species. Doing so will create an egg which must now be protected from scavengers. Once the egg is on the verge of hatching you can enter the creature editor, the first really advanced editor of the game. Here you can spend DNA points to buy new body parts to attach to your creature, as well as modify its appearance. Again, removing parts will buy back DNA points. Points can also be spent on developing the brain of your creature to reach the next stage. For more detailed information on the creature editor see the information page here.
Once your egg hatches you will now control a baby version of your creature, much smaller and with exaggerated features to, well, make it cute. You can now choose whichever play style you wish...will you befriend other species or fight them? Will you group together with other babies to form your own little crew or be brave and go at it alone? Will you explore and be daredevil or stay safely within the vicinity of your elders? Spore's open-ended nature begins to present itself here.
It's safe to say that you won't be getting anywhere without friends. As a mini version of your creature you will need to impress others and get them to join your little group. For those who have played The Sims, the concept is the same. Icons will appear above yours and other creatures' heads showing their responses to your actions. A green smiley is a thumbs up; the other creature likes you. A red smiley is bad news and you're going to have to do better.
What you do with your group is entirely up to you. Attacking other species could bring bad news, especially if they're a social species. Attack one and you'll notice the rest of them gang up against you. The social nature of species from the cell stage is even more present here. You could instead try to make friendly alliances with them. Whether one path or the other offers more benefits is currently unknown. However, the way in which you build your creature in the editor determines its characteristics and abilities. More information is available on the creature editor page.
Finding food (including eggs of other species) allows you to grow until you can again find a mate and create another egg. The process them starts again.
The planet which you are on is populated dynamically by creatures created by other players. The game creates a balanced ecosystem to ensure you're neither the weakest nor strongest creature on the planet. Grow larger and stronger and you'll notice your predators do the same. It's all a matter of staying alive in this dynamic and ever-changing world. This population is achieved through pollinating content which you can read more about here.
Right so you've grown your brain enough to progress to the next stage. Tribal phase, here we come...
(Shamelessly stolen from: Planet Spore)