Add video by clicking on the following symbol: Click image for larger version. 

Name:	video.png 
Views:	1 
Size:	625 Bytes 
ID:	1597 or just putting [ video ] and [ /video ] (without the spaces) around the URL of the video.

The URL is the address of the page you are on when viewing a video.

i.e. http://www.youtube.com/watch?v=U5J5J8k4hH8

You can also get this addrtess by clicking the "Share" button under the video window in Youtube. Make sure the code is highlighted blue then click CTRL and C at the same time on your keyboard to copy it and then CTRL and V to paste it into your post. Alternatively right click the link and use the cut and paste method that way.