Embedding video is quite easy. Once you have your video embed code (can be found on youtube videos by clicking "share" and then "embed"), navigate to your blog post or exercise and click "disable rich text" directly below the 'body' window.
This will strip the text of all formatting options, and leave you with a plain text window. Simply paste in the copied embed code, and then 'enable rich-text' again to see how it looks.
After it is embedded, you can double-click the video player to change its size and alignment.
Save your piece normally and the video will appear whenever the piece is viewed.