Choose Insert, then More Gadgets.
In the Google Sites Editor, find the Insert menu, and open it. You will be able to see a list of gadgets you can add to your site, like Links, Tables, and Images. Find and select the More Gadgets option. This lets you add editable tools such as the POWr Tabs to your page.
Copy and Paste
The Gadget manager will appear. Click Add Gadget by URL. Then add this exact URL into the field. Select Add to finish.
Adjust Height and Width
Now that you’ve added your new, customizable Tabs Widget to your Google Sites page, you’ll probably want to adjust the size and shape of the Widget. Use the different options in the window to select the height and width of your plugin. You can decide to create a title, scrollbar or title around your Tabs Widget, but we advise against it. You'll have more control while editing right through the plugin itself.
Set up POWr Tabs
Go to your live Google Sites website and click the gear icon in the top right corner of the Tabs Widget.
In the POWr Editor, click Import Existing Tabs, find Tabs- and click Copy.