A message queue is a waiting line for messages or jobs that a computer needs to handle. One part of an app can put a task in the queue, and another part can take it when ready.
Imagine a row of order tickets in a kitchen. The cooks can work through them one at a time, even if many orders arrive together.
Queues help separate the moment a task is requested from the moment it is completed. A message may wait for a while, so the app should be able to show whether the task is still in progress.