If you have already installed the add-on, then you only need to create a new page and open the Generator window. Navigate to Pages -> Add New. Then click Insert Shortcode button. In the popup window select one of these shortcodes - heading, tabs, spoiler or quote.
New skins should be already applied here. See screenshot below.
If you still unable to find new skins, you need to clear plugin cache. To do this please just visit plugin settings page, no additional actions required. Just navigate to Dashboard -> Shortcodes -> Settings.