This is the rank you start with. You have basic permissions, and can build in the Survival world.
This one is for people that visit the server frequently. They can build in the Creative World.
Can use TNT in Survival, and works as a mentor and "big brother" for new players. Can /roll a dice. Is whitelisted in case that is ever used temporarily.
Keep the server safe, can kick/ban/warn. Acts as a trusted when there's no mod-stuff to do.
An admin can rollback griefing and use WorldEdit in Creative to clean up.
Manages un-ban requests and promotion/demotions. Can start/stop/restart the server.