The shell is a command line app ( it does not have a GUI interface ) .
Mac
Mac is built on an underlying Unix implementation.
Open the terminal app and start using the app.
Windows
You can enable the Ubuntu subsystem if you have Windows 10 . You can also install a Unix simulator called "Cygwin" .
Select "dos2unix" and "vim" package during installation.
Unix
A shell can be opened on any Unix implementation.