In the View list, select one of the views that show the items or cases available to work on.
Select the case or item that you want to work on, and on the command bar, click Pick.
You also have an option to remove the item from the queue once you pick it up.
When you pick an activity or a case, it gets assigned to you. The Worked By field (in the list of queue items) is also set to you if you leave the activity or case in the queue.