as for all extensions drag the extension into the working area to get the blocks
EDIT: See the App Inventor Extensions document about how to use an App Inventor Extension
Once you have imported an extension component into a project, it will appear in the component palette under the Extensions section. You use the extension component just like any other component by dragging it from the palette to the designer screen, where it will
appear under the designer screen as an non-visible component.
Taifun