Gather allows you to archive multiple items at once or one item at a time. 

To archive multiple items at the same time, select the items you wish to archive. To learn more about how to select items, see this article. 

Then click on the "Actions" dropdown and select "Archive items"

To archive one item at a time roll over the item and click on the file box icon. 

You can also archive a single item from within the item. Just open the item and select "Archive" from the "Actions" dropdown in the upper right-hand corner. 

Single or multiple Items can also be archived from the spread sheet view by selecting the items and then clicking "Archive items" from the "Action" dropdown.