Firstly, be sure that you've added the global tracking code to your website and it is active.
Once you've created your widget, you are taken to the Embed widget screen.
To embed an already created widget, head to the Widgets section and click the "Embed" icon in the "Actions" column.
This is the screen you are presented with:
Embedding the widget is very simple. Click "Copy to clipboard" and paste the embed code into your website exactly where you want the widget to appear.
Head over to your website, refresh the page and as long as you have approved testimonials, the widget will display.