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Are you wanting to delete old documents you no longer need or just delete a page from a Pages document?
Files/documents are deleted from your hard drive in Finder. Click the Mac face in your dock & then navigate to the file(s) you want to delete (probably in your Documents folder). Click once to highlight & then go to File > Move to Trash or type ⌘ + delete.
If you're wanting to delete a page from a Pages document, please post back & someone can give you detailed information.