This is the start of a video series explaining how development using a REPL (command line) based development works. I made this primarily as an intro for people used to advance Integrated Development Environments IDEs such as Visual Studio, IntelliJ IDEA, Xcode or Eclipse and who are curious about how people manage to do any coding with just a simple text editor and command line. This is also meant for Python and Ruby developers who want to know how the Julia REPL is different.