How can I manage folders and files using rest api?

How do I use rest API to pull data from folders and files? Each set of files are associated to one particular folder. I'm not sure how the are associated and I need to pull certain fields associated to the folder and another set of fields associated to the files.

Is there a way to get the a specific row of items and expand it so the children are available.

The following appear to work, but I do not see the relationship to make one or more calls and associate the folders with the files.

_api/web/lists/getbytitle('production_library')/items?$filter=Business_x0020_Process%20eq%27Communication%20Management%27




_api/web/GetFolderByServerRelativeUrl('production_library/Communication%20Management')




_api/web/GetFolderByServerRelativeUrl('production_library/Communication%20Management')/files




_api/Web/Lists(guid'85d38c8f-9ba0-426e-862e-c0497a1af706')/files('KYiffOP-8Ee2mLxLXncH7uKIVxdXGr9Ftvg6up7WivC7Rc5Eb5v8Rq9Aq-cSEEqN')/Children