You have to be logged into the forum. When you create a new forum topic, you will see a new BBcode named youtube located just above the message body box where you type in your new message. Just click on the youtube BBcode box and then enter the web url address of the YouTube video between the youtube BBcode boxes in the message body box where you are typing your new message.
example: [youtube]Link to YouTube Video[/youtube]
That's all there is to it
