McMMO is experience you have in something. There are Swords, Woodcutting, Archery, Acrobatics, Salvage, Smelting, Unarmed, Taming, Axes, Repair, Alchemy, Mining, Herbalism, Fishing, and Excavation. The more experience you have the more special abilities you get. For example, depending on your mining level and experience you have you will earn super breaker for longer periods of time as well as a triple drop chance. Another example is swords. Depending on the experience you have with swords it will allowed to add bleed effect on players you attack as well as counter the opposing players hits. You can check your power level and the amount of experience you have by doing /mcstats. I hope this helped!