Spermicide is the name of the game in Ovar.io. Choose from 1 of 5 classes of sperm, and then wrest control of the ovario-filled waters, making as many babies in the process as you can .
Guide your sperm with the mouse, and hold the left mouse button to use your special ability, depleting your special meter in the process.
From there, it's a game of harpooning enemy sperm through the tail in order to kill them, and capturing as many ovaries as possible as they spawn. Just tunnel your way to the center.
Level up your stats by collecting the pick-ups littered about the map. The bigger ones are power-ups; don't miss those.
You can top the scoreboard pretty easily by avoiding sperm, leveling yourself up, and making as many babies as possible. Killing other sperm is just icing on the baby-cake.