A Queue is a group of Tickets in RT that are logically related. All issues in a single Queue can be handled by a more-or-less homogeneous group of people inside an organisation (like the people in the sales department, or a group of people that can deal with customer requests for software licenses, or the service department).
A very good rule of thumb for RT system managers is: when you find yourself regularly adding or removing queues in the system, you are using the wrong concept of queues. The queue system in RT mirrors the organisation that uses that instance of RT, and normally the organisational structure does not change very often.
The Rights system in RT can allow users or groups of users different rights on different queues. This makes it possible to hide developments in the R&D department in a company from the Sales force, but also to allow service people to check on sales issues if this is desired.