What is the queue concept in computer system?

It's very similar to real-world queues. Queues can be used for various purposes. For example if there are multiple tasks that are waiting to be executed, then they will wait in a queue for their turn to come. Another use is when some resource (say your printer) is needed by various tasks for their successful and complete execution. These tasks will then wait in the queue for their turn as each task in front of them uses and releases the printer and then exits the queue.

Basically a queue is a First In First Out (FIFO) structure. This means, that like real-world queues, the first task to enter the queue will be the first to execute or obtain its required resources. Any other tasks that come after it are added to the rear end of the queue and from there they move to the front of the queue one-by-one as their turn comes up.

Hope that helps.