How can I match completely the formats on separate word documents? (These are the various tales in a book of short stories. One document per story). Can I decide a format for one document, and then apply it to new blank documents, or to others already with content.
I mean everything: headers footers, margins, font, size, line spacing etc


If I do nothing, the various documents seem to end up with slightly differing formats.

You need to become familiar with the idea of Templates. Templates in Microsoft Word
Take a document that has the formatting you want and save a copy of that as a template. Erase the content. Use that template as the basis for your other stories.

For ones that are already written, you can use the template to create a new document. Then copy the content from the existing story into the new document and save that.

Dear Charles Kenyon
Thank you very much for this. I will study your tutorial over the holiday.
Merry Christmas
Richard Buckley

You are welcome. It is a lot to take in in one sitting, I know. Enjoy your holidays.