Levels are used within networks and chat rooms to control access to various features and moderation capabilities.
Here is a general meaning for each level:
Owner This is someone who has created the network or chat room, or at least has the private key. They can do anything. They are usually hosting the chat room or network on their computer (unless there are multiple owners).
Manager This is one step under the owner, and can alter the network/room information and configuration, which includes the name, description/topic, and several of the configured operation parameters.
Operator This level is meant to be for users that have oversight over the moderators, with the ability to appoint and demote them at-will.
Moderator Moderators have the power to change the level (including ban) of any user that isn't also a moderator or higher.
VIP / Star / Trusted These are above-normal levels meant to signify users that are more trusted or valued than others. In chat rooms, they will have special icons to denote this. Also, networks/chat rooms may be configured to give additional privileges or bandwidth allowances to users at these levels.
Normal This is the usual level for most users.
Basic This is like the Normal level, but on networks with a default configuration, these users are not allowed to share files.
Silent These users are not allowed to share files, and are also muted in a chat room.
Banned Can not connect to the network / chat room.
A user's level can be only be changed by a Moderator or higher, and they must be of a higher level than the target user. Therefore a moderator can not change the level of another moderator. The only exception to this is with Owners. An owner can adjust the level of another owner. But if an owner is in possession of the private-key, then the next time they connect, their level will go back to owner.