Well, indeed. Lulu is a site for the use of self-publishers of e-books and printed books, with the option of free ISBNs to get them Distributed across all on-line book stores.
Yes, you have to create files on your computer. One for the pages, and at least one for the cover. Once you are happy with them, you open a Project Wizard to upload them in to. I do not know about Mac Pages. Will it Save As a PDF or a Word docx? because that is what Lulu's Project Wizards use. To be safe I would get Word if I was you, then the docx may be compatible with Lulu's Project Wizards.
I think you typed the wrong size. This is what you can do here >> http://www.lulu.com/create/books
And this is where you will find a lot of help >>> http://connect.lulu.com/en/categories/print-and-ebooks/sso?_ga=2.191111458.944120412.1539662034-2066720930.1539662034