Its real easy. What i do is have rollitup open then open up the internet again and go in to youtube so i have 2 browsers open at the bottom of the page that i can alternate between so i go into youtube and find the video i want and when its found you simply right click on the very top toolbar that shows the code of the video then choose copy. The code will look like this.
http://www.youtube.com/watch?v=lgT1AidzRWM
Then turn that or any address in to [youtube] lgT1AidzRWM [/youtube ] (no spaces)
So its basically [youtube] the code [/youtube ] (no spaces)
Where i have put spaces in the address to demonstrate is just to provide a space as there are no spaces its everything (the code) after the = sign on the youtube link in between the start and end [youtube] *********** [/youtube ] (no spaces)
Hopefully that helps a little and if you can send me a youtube address i will turn it in to the video.
(good luck).