The Client Testimonial section of the home page uses a Web Savvy – Featured Video widget. To configure this go toAppearance –> Widgets and drag one of the featured video widgets over to the Home Main Section widget area. Then configure the widget as desired.
In the YouTube Video URL field enter the full URL for the YouTube video you wish to display.
You may either paste the URL of your Cover Image directly into that field or use the Upload Image button to select an image from your WordPress Media Library. For best results we recommend using a Large size image that is approximately 1024px wide by 576px high.
Here is how we have the widget configured in our theme demo:
(Our forum software is garbling the code so you can find it in the Gist at the above link.)
Here is a screenshot of the widget configuration:
The theme is coded to be able to use any of the video sites included in the WordPress core oEmbed functionality. Please see the WordPress Codex page about oEmbeds for a full list of compatible video hosting sites which can be used in the featured video section.