MoAR is designed to have two playable modes: Arena and Survival.
Survival Mode is straight forward. You choose the hero you want to level up, and fight off waves and waves of enemy AI and use the kills as credit to buy new abilities that can eventually help you to get more kills.
Arena Mode allows players to fight against other players. You can use the abilities gained from playing the Survival Mode to play in this mode, however, kills are more valuable gained in Arena Mode and is also redeemable for purchasing new abilities and new heroes. The same ability that will require 1,000 Survival Credit will require 50 Arena Credit.