Hello World is ubiquitous in computer programming. It's a bit like saying, "Testing, one, two, three," into a microphone. When testing out a programming language, you write a tiny program that merely prints out the words "Hello world."   The dark panel on the left is Terminal, Mac's version of an app-type commonly referred to as the command line, or console, or, less-frequently, shell script editor. The panel on the right is Atom, a text editor for writing programs. To run a Java program, you have to save the .java file somewhere on your computer, open Terminal, navigate to that file, compile it, and run it.   REAL LIFE NOTE:  These tasks sound simple, and they are -- I promise once you know what you're doing, they really are -- but for a first-timer, simply being told to log in to a new computer can be daunting. Trust me, I've been the student, and I've been the teacher in the comp sci department at my university. I can't recall exactly, but it's very possible that our first 50 min lab consisted of simply creating and running HelloWorld.java. SaveSave