It is a customizable toolbar placed beside the quick access button and on top of the home tab. once you click the down arrow at the end of quick access toolbar it displays a lot of commands. You’ll be able to add any of those commands to quick access toolbar by a left click on the command.
You can also add often used commands from office button and ribbon to quick access toolbar. To feature a command, right click on that then click on “Add to quick Access Toolbar” possibility. The command is going to be additional too quick Access Toolbar.
See the image given below, once a right click on the Paste command, we tend to get four choices, out of that we will select the choice “Add to quick Access Toolbar” with a left click.