Choose Insert, and then More Gadgets.
In the Google Sites Editor, find the Insert menu, and open it. You will see a list of components you can embed on your site, like Tables, Images, and Links. Find and select the More Gadgets option. This lets you add editable tools such as the POWr Image Gallery to your page.
Copy and Paste
The Gadget manager will appear. Select 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 Image Gallery Widget to your Google Sites page, you’ll probably want to adjust the size and shape of the Widget. Using the options in the pop-up, pick a height and width for your plugin. You can decide to create a title, scrollbar or title around your Image Gallery Widget, but we advise against it. You'll have more control while editing right through the plugin itself.
Set up POWr Image Gallery
Go to the live Google Sites website and click the gear icon in the top right corner of your Image Gallery Widget.
In the POWr Editor, click Import Existing Image Gallery, find Image Gallery- and click Copy.