Whether on macOS or iPadOS, you will need to sign into iCloud with your Apple ID in the Settings (Preferences) panel.
In Finder Settings (or Preferences) > Sidebar, select iCloud Drive and Shared items under iCloud. This will display those two items in the left panel of a Finder Window where you can drag and drop Pages documents while on the Mac. Signing into iCloud also makes iCloud Drive available to the Pages application for opening or saving documents on the Mac.
On the iPad, you will need to visit Settings and sign into to iCloud. Then the iPadOS File application will allow you to see Pages documents on iCloud and/or your iPad local storage. You can even copy/move them from iCloud to your local iPad storage if desired. Pages for iPadOS will also be able to access your Pages documents whether on iCloud Drive, or local to the iPad.