Example — pwd
This command works on Windows, Mac and Unix:
pwd
It means “print working directory” and will show you the full name of the directory you are in (strictly speaking, the whole “path”, or address in the file system).
So type pwd
and hit enter.
The computer looks at your command and sees if it knows a command with that name. It does, so it executes it: it prints out its answer, and then it’s finished. Because it’s got nothing more to do, it throws up a new prompt for you.