@Jamesgang , if you have videos loaded to youtube already, make sure they are public and not private. Anyone should be able to go on YT and view it.
When you view any video on YT, it has a url, that's the
http://*******. Just write that down. Then when you come into this forum and want to post a video, hit the link button up there in the toolbar. Looks like a little chain, just to the right of the A. That will prompt you to enter the url, enter it entirely and then preview your video.
Probably the hard way but that's how I do it.