Quick Access Toolbar in Excel
It is a customizable toolbar located beside the quick access button and above the home tab. When you click the down arrow at the end of quick access toolbar it displays more commands. You can add any of these commands to quick access toolbar by a left click on the command.
You can also add frequently used commands from office button and ribbon to quick access toolbar. To add a command, right click on it then click on "Add to Quick Access Toolbar" option. The command will be added to Quick Access Toolbar.
See the image given below, after a right click on the Paste command, we get four options, out of which we can select the option "Add to Quick Access Toolbar" with a left click.