@saab,
You did everything right except that you failed to type / before the second youtube as in [/youtube]
Simply type [youtube] then again but with the stroke [/youtube] and insert your link. I did it below using the link you posted - all I did differently was the / before the second youtube. And yes, you can use [img][/img] and change the letters at first - I did when I first started posting. But once you get used to it, you'll find it's easier to type the whole thing yourself.
Sorry if I'm not very good at explanations!