Below is a video of youtube's video page. Find the link that says Embed.
( I added red X's to the below video so you can easily find it.)
You will have to click on the “use old embed code” on the Youtube embed code options.
Click in the Ebeded Link text box and then right click and then click copy.
You will have to click on the “use old embed code” on the Youtube embed code options.
Add embeded video link to post.
At the bottom of the forum pages above the post text box you will see a button called "Add Embeded Video Link"
Click the "Add Embeded Video Link" button and the Embed Video Link Text box will appear.
Left click in the Embed Video Text Box. The right click and click Paste.
If you are adding a new post then you will need to add a Topic and add a message to the Post Text box.
Click the "Post Message Button" below the Post Text Box.