A point and click game. I'll let the game makers describe it for you.

Move your mouse to move your microbe. You eat proteins, which make you grow, and give you Action Abilities. You receive Action Abilities when Allied Microbes eat proteins, too. Action Abilities are used by clicking on the icon, or the corrosponding number on yoru keyboard. If you are the proper size ratio, you may eat an enemy microbe. Eating your enemies will also increase your size. An enemy will grow in size as they eat proteins and microbes, too. Once a microbe gets to a certain size, it can split in two. This can increase the number of allies, but make you smaller and more vulnerable to an attack. Use it wisely. Viruses can infect you and your enemies, and disallow use of your Action Abilities, and eventually kill you. In order to win, eat/destroy enemy microbes.--Taken from the front page of the game.

Good luck.