After creating the contest you purchase your promotion. Then, click on the "Publish" button for Facebook Page under the Publish tab. After you click on "Publish" [you would be required to log into your Facebook account if you are not already logged in] a list of Facebook pages that you administer will populate the menu. You can select the page that you want to Publish the contest to by clicking on "Add". The contest would be published to the selected Facebook Page.