For example:

Check out this cool video:

That was a cool video.

WordPress will automatically turn the URL into a YouTube embed and provide a live preview in the visual editor.

Another option is to wrap the URL in the </code> shortcode. It will accomplish the same effect, but does not require the URL to be on its own line. Using <code></code> allows for the inclusion of a maximum (but not fixed) width and height: <code>...

If WordPress fails to embed the URL, the post will contain a hyperlink to the URL