Apple File System (APFS): The file system used by macOS 10. To open a window and see the files on your Mac, switch to the Finder by. Use Finder, the macOS file manager, to work with various files on your computer. You open files every time you work on a Mac, and there are many. It aims to fix core problems of HFS+ (also called Mac OS Extended), APFS's predecessor on these operating systems.