Did you actually read it?
Originally Posted by kiwidude
7. By default a GUI action plugin will not appear in any menus or toolbars. To add it to any of these you must go to Preferences->Customise the toolbar. In the dropdown at the top choose where you want the new "action", such as "The context menu for the books in the Calibre library". Select the new plugin within the "Available actions", click the add button and move up/down as required.