To embed a YouTube video into your Duplie site, you first need to find or create the page you want to embed the video into. Pages are managed in: Site and then Pages/Links. There you will see a list of pages on your Duplie instance.  You can either create a new page or open an existing page.  If the page shows custom content, you should see a list of widgets on the left.  Drag the YouTube widget and you should be prompted with a modal to enter the video URL.  Paste in the YouTube URL and save.  The video should now display when a user visits the page.