Vim Basics
Vim isn't necessarily everyone's favorite editor, but on remote servers it's often the most readily available tool. Knowing at least how to enter edit mode, save, quit, and search can save you from a lot of awkward moments when you first connect to a server.
This material doesn't need to be studied as an advanced Vim tutorial all at once. Start by getting comfortable with the most common editing actions, then gradually add shortcuts and configuration later.