Where are Photos photos stored on a mac?

They are stored in the Photos library file as a package if you are copying the photos to the library. Right click on the library file and Show Package Contents. This file is normally stored in your Pictures folder. Do not manually change any info in the library file.

If you are using a reference library, then they will be stored in a location you choose as files and folders in the finder.

Gotta be a folder or folders where the photos in the Photos app are stored. Where are those photos stored?

By default are the photos inside the Photos Library Package. The default location of this package is in the Pictures folder.

See this Help page: Where are my imported files? https://help.apple.com/photos/mac/1.0/?lang=en#/pht12e7a8015

Masters is your originals.

The Modified and Originals were links to older iPhoto libraries.