Something like this:
Take the following YT URL:
http://www.youtube.com/watch?v=K8E_zMLCRNg
Take the last characters (K8E_zMLCRNg), go to "Edit Your Details", scroll down to the YT thing, and then paste something like this: v/K8E_zMLCRNg.
Of course, you don't have to use what I just did, and there's a better example in the "Edit Your Details" anyways XD