Why we use Queue & Can i implement CIR using Queue?

Hi
I am new to Mikrotik. Why we use Queue and how can i make my network better using Queue. If i want to assign CIR connection to specific user, Can I?

Queues are used to limit traffic, or traffic shaping, or prioritize traffic.
You can use queues to configure CIR. To do that you need to specify
limit-at and max-limit in queue. Limit-at means that the traffic should never
go below that value (of course if bandwidth is available), and that is CIR.

You can have a better look at wiki http://wiki.mikrotik.com/wiki/Manual:Queue