In The Outliers, Bill Joy is quoted as saying
"If you put your Mac in that funny mode where you can see the code, I see things that I can remember typing 25 years ago."
I'm intrigued - what is this mode? How does one use it?
Single user or Verbose mode.
You have successfully entered verbose mode when you see white text appear on the screen.
See Apple Support
There's no such thing (from the user point-of-view). Mac OS X is not an open-source operating system.
More than likely, He is talking about single user mode. Single user mode is a state of the operating system used to repair functionality of the operating system.