First you'll need to link your Pixorial and Facebook accounts. You can do this by going to your email address at the top of the screen, then Social Networks, and selecting Facebook from the drop down. Then click the "Connect with Facebook" button. Follow the steps to log in and then your account will be connected. In the event that you're told the account is already connected to another Pixorial account (and you don't know which) or you encounter any other errors attempting to connect the accounts, please contact customer service.
Now that the accounts are connected, you'll need to select the video in your Pixorial library. Select the "Action" drop down and you'll see the option for "Facebook" appear. Once selected a popup will appear and allow you to add a comment or change the title of the video. Select "Post" and your video will be on its way!