The QAT is a toolbar, by default displayed at the top of the window, providing access to mostly used commands:

Generally speaking, the Ribbon control is not customizable. An end-user is not able to change the position of commands or hide them. However, it's possible to copy your favorite commands to the QAT via a context menu. So you'll always have a quick access to these commands:

By default, the QAT is displayed at the top of the Window. Using the Ribbon control's context menu, you can move the QAT below the Ribbon commands region.