When you import the photos to Photos, they are stored inside the Photos Library. The library is a package of folders and linked database files, shown by the Finder as just one closed item. Even if you open this package with "Show Package contents" you will not be able to find the photos inside easily in the Finder, because Photos is renaming the files internally. And if you are using iCloud Photos the original photos may not be even mirrored on your Mac but only stored in iCloud.
To access the photos use the Photos.app to pass them to other apps or to export them to the Finder or use the Media Browser to show you the Photos Library in other apps. When you try to open from another app, the file chooser dialog will show you window, where you can scroll down in the sidebar to "Media > Photos" and click the Photos Library to browse it.