To place a video from YouTube onto your website, you "embed" the video, copying and pasting the code provided by YouTube into your WordPress or Sitefinity editor using the HTML view.
The first 4 steps are shown here:
5. On the page and location where you want to place the video, in HTML view, paste the code in the proper location
6. Save the page
7. View the page on the actual web page (not in the editor) to verify it appears as you wish