Canceling

Click on the "■ Stop" button near the bottom of the window's center column to halt pending operations.

When only one transaction is active and none are queued, it will be stopped immediately.

If multiple transactions have been queued, the current transfer will continue while you are prompted with three options:

The current transaction will continue while you are deciding, but no new transactions will be started until you have answered the question.  Leaving this dialog open effectively pauses the queue, allowing you to continue later.

Some kinds of transfers can be resumed from the point where you stopped them, while others will need to start over from the beginning.  See Resuming for details.