This guide applies to all MacOS devices such as iMacs (Standard, Mini), MacBooks (Standard, Air, Pro)

  1. Click on the [Apple] icon at the top left hand corner
  2. Click on the [About This Mac] item
  3. Look at the [Version] field

You should now see the information about the MacOS version you are using, i.e.: Version 10.13.6 (17G65)