Your video Card (in the 'Build Your Own' section) will support videos hosted on Vimeo, Youtube or Wistia.
Just select your source, and enter the last part of the URL for the video.
For example, 'https://www.youtube.com/watch?v=rqQPAzuGxyU' would be shortened to 'rqQPAzuGxyU' and entered into the video source box:
That's all you need to do! Flip the Card and you'll see your video ready to be played within your Board: