In Gota.io you grow by eating other cells and other players who are smaller than you. This game is clearly based on Agario, but will run faster for some people! Start with a basic colored cell - move around the map using your mouse and collect the various colored cells that are scattered on the ground - as you collect cells, your own cell increases in size.
Aside from collecting cells, you can also use the W key to eject your mass - use this to dispel some of your own cell to then eat it again and gain a boost. Alternatively, use the space bar to split your cells into several smaller ones - this allows you to collect cells from a wider area. Try to dominate the arena and don't forget to talk in the group chat and have some fun!