McMMO is the skills plugin that allows you to level up in skills like "herbalism" and "woodcutting". Levelling up each skill unlocks several skills like "Double Drop".
To redeem credits do /redeem <skill> <amount>
To check your credit balance do /credits
To view a skill do /<skillname> E.g. /herbalism
To get a list of skills and your levels in each skill do /stats
Viewing Level Bonuses E.g. Double Drop
To get to the skill, do /<skillname>
There are skills shown at the top. Some of them can only be accessed by levelling up that skill to a certain point while others are percentage-based and increase over time.
Viewing another player's stats
To view the skills of another player do /inspect <playername>
Toggling McMMO Abilities
To toggle the activation of McMMO skills upon right-click with an item in your hand. I.e. pickaxe or axe. Do /mcability
Displaying list of McMMO commands
To access the full list of commands do /mcc
Viewing McMMO help text
To view the McMMO help text, do /mcmmo