Susan,
You need to create a pdf file of the document to print using CreateSpace. Check their size requirements and set up your document to fit those, make sure your cover has the correct bleed if the cover image goes "off the edge", and work your way through the guided system on CreateSpace. If you know someone who has done a book there, they might be able to help you, too. I will be doing a book from an author who used Pages soon, too, and though I use InDesign, he does not. I don't anticipate any problems with it, as a pdf is a file structure with which CreateSpace is familiar.
You can also use their more tutorial-like set-up, too, perhaps, at least the first time through the process. I typically help first-time users through the process when I've helped create their books, too. It's mostly straight-forward, minus the upload problem I'm currently dealing with with my computer, of course!