OK, so you want to link a YouTube video, and you'd like it to show up in your text? Cool, so do we!
Fortunately, it's very simple. Firstly, find the URL of your video. It will probably look something like this:
http://www.youtube.com/watch?v=eIl1VuGTk3g&feature=relmfu
or this:
http://youtu.be/eIl1VuGTk3g
If your URL is of the first format (the long one), then simply paste it into your post; then highlight the entire URL including "http" (see 1st attachment, green circle), and click the "YouTube" button, just above the first smiley face (blue circle in 1st attachment). This will surround the URL with YouTube tags, embedding the video, thus:
[youtube]http://www.youtube.com/watch?v=eIl1VuGTk3g&feature=relmfu[/youtube]
For the shorter version of the URL, just paste the bit after ".be/" and click the YouTube button:
[youtube]eIl1VuGTk3g[/youtube]
The results are an inline video:
Enjoy
(Edited to make more sense...)