Embedding YouTube/Twitter/Facebook/External Content
To embed content from external websites, simply paste the URL and then press enter. For example, you can copy and paste this URL from YouTube:
https://www.youtube.com/watch?v=dQw4w9WgXcQ
Iframe embedding is also possible by pasting <iframe> embed codes. For example, copy and paste this embed string:
<iframe width=”560″ height=”315″ src=”https://www.youtube.com/embed/dQw4w9WgXcQ?rel=0″ frameborder=”0″ allowfullscreen></iframe>
You can embed URLs from sites listed in the WordPress Codex: https://codex.wordpress.org/Embeds and any oEmbed enabled site.