To embed a YouTube video you should:

1. Hit the share button on the video you want to embed
2. Choose the Embed option
3. Press the copy button to copy the embed code
4. Add an Embed component in the CMS on the page you want the video to appear on
5. Paste the Embed code into that component
6. Replace the first part of the embed code that reads 

   <iframe width="560" height="315" src="https://www.youtube.com

   with this:
   <iframe width="1280" height="720" src="https://www.youtube-nocookie.com
7. Save and preview the page to test it works!

This video explains in more detail: