Is your Mac operating system up to date? Does it meet the system requirements of an app or device that you want to use with your Mac? Which macOS versions are earlier or later than the version you're using? To help answer these questions, you need to know which macOS version you're using now.
Check About This Mac
From the Apple () menu in the corner of your screen, choose About This Mac. The version of your operating system appears next to “macOS” or “OS X” in the window that opens.
Below is an example of macOS High Sierra