Gadgets are additional tools and plug-ins that you can emebed in Google Sites. Many of these plug-ins are created by third-party groups not affiliated with Google or UW, so make sure that you know what each gadget does before placing them on your site.
To embed a gadget, go into 'edit mode' and click on the Insert menu. Scroll down and select the More Gadgets item.
A pop-up box will open with a list of gadgets that you can place in your site. You can select from featured to popular gadgets and various gadgets from websites that support Google Sites.