Click on the Apple on the top left of the screen and then click AboutThisMac.
The macOS name and version number will be displayed on the screen.
Windows
There are a few ways to identify what version of Windows you are using.
Using a keyboard shortcut
Hold down the Windows key and while continuing to hold down that key, press the Pause|Break key.
This will open the Windows System screen which shows you the version of Windows you have.
Manually open the System Information window
Using the Right mouse button, click the Start button and select System from the menu that opens.
If you do not get this menu, using the Left mouse button, click the Start button. Then using the Right mouse button click the Computer menu option. Then click Properties.
This will open the Windows System screen which shows you the version of Windows you have.
Looking at the start button
Windows 10
The default Windows 10 start button looks like a square divided into 4 smaller squares that is slightly slanted towards the left.
When you click the Windows 10 Start button, it brings up a menu that looks like the menu on the left. It also has the words "Ask me anything" or "Search the web and Windows" next to it which is unique to Windows 10.
Windows 8.1
The default Windows 8.1 start button looks like a square divided into 4 smaller squares that is slightly slanted towards the left. It is almost identical (though slightly bigger) than the button in Windows 10.
The biggest difference is that when you click the start button, instead of opening a menu it typically takes you to the Tile view of Windows (seen below).
Windows 7 (No longer supported at Hofstra)
The default Windows 7 Start button is a circle with a Windows flag inside. The Windows flag is very colorful and wavy. It also has a bit of a glow to it.
When you click the button, it opens a start menu. Right above the start button it says "Search programs and files." That box with those words appears to be unique to Windows 7.
Windows Vista (No longer supported at Hofstra)
The default Windows Vista Start button is a circle with a Windows flag inside. The Windows flag is very colorful and wavy. It is a bit duller and darker than the Windows 7 start button.
When you click on it, it opens a start menu. Right above the start button it says the words "Start Search." That box with those words appears to be unique to Windows Vista.
Windows XP (No longer supported at Hofstra)
The default Windows XP start button is a green oval that says Start in white letters. If you are using the default them, the start button is typically green and the taskbar is typically blue.
When you click it the start button the start menu opens. The start menu for Windows XP has the Run button by default (bottom icon on second column of start menu) which was removed from later versions of Windows.