Which version of Windows 10 am I running? Find out in 15 seconds!

To find out which version & build of Windows 10 you are running, first press Windows key + R.
This will open a command prompt:

In that dialog, enter winver:

Now press Enter (also known as Return). This will open the version information window, for example:

In that window, you can immediately see the version & build you are running, highlighted in red:

In my case that is Version 1809 and Build 17763.475.