For the most part, users running Photoshop on a Mac vs on a Windows-based system will find the differences within the application itself negligible and transparent. There are dialog boxes that might look different due to the various Operating Systems but the functionality and choices within those dialog boxes remain the same. There are some keystroke command differences as well. Use this handy reference to help:
WIndows CONTROL = Mac COMMAND
Windows ALT = Mac OPTION
Windows BACKSPACE = Mac DELETE
So one example of these differences would be to Open a New File. On a PC the user could use the shortcut key combination CONTROL N on a Mac the user would instead choose COMMAND N.
-Thanks to Joan Sides!