If you followed the instructions on how to add creative, you will end up on the creative management screen. Now just click the green '+ page' button to start adding pages:

• Give your page a title (must be unique; you can always change it later).
• Enter an optional description.
• Select a master page for the page style. This will be the template that allows you to add your content to the page.
• Hit the save button.
• You can keep adding blank pages, or you can start adding content to your pages.