If you amit filling the Page ID field, the pop-up window will be displayed on the front page, to display it only on several chosen pages provide a list of post IDs separated by the space character, for example: 22 95 8 4, or only one post ID if you want it to be shown on a single specific page.

You can look up the post ID of a page by following these steps:

  1. use the 'View Page Source' option in your web browser, to see the HTML code of a giving page
  2. find the opening body tag (you can use <body string in the search field) there you'll see a list of CSS classes, you'll see the ID of a page/post as a number among these classes.