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
Click image for larger version. 

Name:	shareyoutube1.jpg 
Views:	6 
Size:	20.3 KB 
ID:	895


The next step is to insert it into your post. You simply do this by clicking this little icon....
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Name:	shareyoutube2.jpg 
Views:	5 
Size:	13.2 KB 
ID:	894

Paste it in the space provided....
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Name:	shareyoutube3.jpg 
Views:	5 
Size:	15.7 KB 
ID:	893

and YOU ARE DONE!!

Your video should appear like the one below.