You are Og. The object of the game is to stay alive as long as possible, collecting as many points as you can along the way.
You collect points by eating things. Under normal circumstances you can eat anything EXCEPT for Breakers and RadZones. Breakers and RadZones will take away Shields if you run into them - or, if you are out of Shields, you will die.
If you eat the Runner, you get energized. When energized, you can temporarily eat ANYTHING you like. Use this power to help you clear away excess clutter. RadZones in particular can be worth a LOT of points.
If you eat the Letterman enough times that you manage to get ALL of the letters in the word "BREAKER" highlighted at the bottom of the playing screen, you will be richly rewarded and given the power of... the OgBurst!
You get 3 lives to start. You receive an extra life at 50,000 points and then every 100,000 points thereafter. (i.e. extra life at 50,000 points, 150,000 points, 250,000 points etc.)