First, you will need to click the "Share" button under the video you want to share from your YouTube Account.

Once you click share, you will see a unique URL like this one: http://youtu.be/4odbAlDRiz0
-shareyoutube-jpg

The next step is to insert it into your post. You simply do this by clicking this little icon....
-shareyoutube2-jpg

Paste it in the space provided....
-shareyoutube3-jpg

and YOU ARE DONE!!

Your video should appear like the one below.