You just need to put the part of the url after the v= between bracket YT tabs. For example, from the last thread you posted in:
the URL is: http://www.youtube.com/watch?v=i-G0BvvagrU
The part you need is: i-G0BvvagrU
Then, with square brackets (instead of the curly ones I'm going to use so you can see it) you enter: {YT}i-G0BvvagrU{/YT}
And it looks like this:
https://www.youtube.com/watch?v=i-G0BvvagrU
Hope this helps!