Choose Insert, then More Gadgets.
In the Google Sites Editor, open the Insert menu. You should see a list of available components and gadgets you can add to your site, like Images, Links, and Tables. Select More Gadgets. This will allow you to add customizable tools like POWr Online Store to your site.
Paste in URL
You will see the Gadget manager. Choose Add Gadget by URL. Then paste this URL into the field. Click Add to finish.
Change Height and Width
Now that you have embedded your new, fully customizable Online Store Widget onto your website, you'll probably want to change the shape and size of the Widget. Use the options in the pop-up to choose a height and width for your plugin. We don't recommend it, but you can insert a scrollbar, title or border to your Online Store Widget. You’ll have more editing controls directly through the plugin.
Set up POWr Online Store
Go to your live Google Sites web page and select the Settings Icon in the upper right corner of your Online Store Widget.
In the POWr Editor, click Import Existing Online Store, find Online Store- and click Copy.