Choose Insert, and then More Gadgets.
In the Google Sites Editor, open the Insert menu. You should be able to see a list of available gadgets you can install on your site, including Tables, Links, and Images Select More Gadgets. This will allow you to add customizable tools like POWr Flickr Gallery to your site.
Paste in URL
You will see the Gadget manager. Click on 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 Flickr Gallery Widget onto your website, you'll probably want to change the shape and size of the Widget. Using the options in the pop-up window, choose the height and width of your plugin. We don't recommend it, but you can insert a scrollbar, title or border to your Flickr Gallery Widget. You’ll have more editing controls directly through the plugin.
Set up POWr Flickr Gallery
Go to the live Google Sites web page and select the Settings Icon in the upper right corner of the Flickr Gallery Widget.
In the POWr Editor, click Import Existing Flickr Gallery, find Flickr Gallery- and click Copy.