There was a day when computers didn't have a graphical user interface (GUI) and you had to do everything directly in the command line.
Yes, even text-editing. No Microsoft Word, Notepad, or whatever code editor you like to use.
That means you either had to use nano, emacs, or vim.
My personal favorite is vim because (objectively-speaking) it's the best. Once you get the hang of it, you can be incredibly proficient with text editing.
Even when I use IDEs like IntelliJ or VS Code, I use the Vim-plugin, which makes the editor Vim-like so I can take advantage of the increased speed of editing.
Comprehensive Vim Guide
Introduction to Vim
Part 1: Bare Minimum
Part 2: Navigating
Part 3: Editing