How do I set up pages for mac and ipad to share a document and keep them synced.

There is currently no capability- you will have to wait for Mountain Lion this summer for that feature.

You can upload them from Mac to iCloud and then download on the iPad. They only directly sync between iOS devices. The Mac version of Pages has more options that are not available on iOS. If you use a font that is not available on iOS it will change the font. Some layout options aren't available either.