Click on the Quick Access Toolbar

If the commands you require are not visible, then select More Commands

In the Choose commands from bar choose Commands not in Ribbon (Menu). A list of all toolbars not available on the current menu will be available.

Choose a toolbar and click add

This toolbar will then be available on the Quick access toolbar.

In the Categories box (on the left-hand side) click on the category of icon that you want to add (e.g. Insert)