How was a shell like when operating systems didn't had a GUI?

I understand the concepts of terminal, console, shell and their differences. I know a shell today is an interpreter that communicates with the OS kernel to perform some actions and does it through terminal applications. But in the old days when computers didn't had GUI, all the interaction a user had with a computer was through the shell? I've read that the Bourne Shell (sh) was introduced in Unix version 7, was that like, you turn on the computer and from the moment you start typing you are communicating with sh? or you had to enter the sh program through a command and then that shell starts? And kind of the same with windows or Mac, is that MS-DOS functionality what we have today in cmd? Thanks in advance and if someone can leave a documentation where this evolution is explained I'll be very grateful.