An agent can choose which queue to join and they can be a member of more than one queue. In this case, the panel can be used to select which individual queues an agent will be logged in to.
Use the 3CX Web Client to log in and out of individual queues:
The explicit login and logout can also be done on behalf of the agent, by the assigned queue manager(s). Agents who are not queue managers can only log themselves in and out of queues.