Agar.io or Agario is a game in which you take charge of a tiny cell, eating small dots and other players that are smaller than you. Every time you eat a dot or another player you grow in size, making you more dangerous, but also slower.
Agar.io has an incredibly simple premise – name your circle, guide it around, eat dots and other players and grow larger. But it is made more complex by the ability to divide your cell in two to make quick getaways or to mount fast attacks on other players. In the team-play mode you can feed some of your mass to other players or just play entirely for yourself. Each time you are eaten you begin again at the bottom of the food chain.
If you cannot connect to the servers, check if you have some anti virus or firewall blocking the connection.