Welcome,
sounds like you're asking "how do I use an editor", and what can you do when there is no graphical interface.
A game engine is hardly the right place for this, we work with any editor we like, or the one that comes with the engine.
You're on Windows apparently, so there's always a mouse and graphics for user interaction, not sure if it is even possible to use Windows without a mouse, or other input device like touchpad etc.
When you choose an editor, make sure that it allows for entering plain text without any formatting. MS Office or what it's called these days is not the right tool, but mousepad for instance is. Also so called IDEs (Integrated Development Environments) like Visual Studio, Codelite, Code::Blocks, and a ton of others can be used to write program text. If you're more into command line tools, have a look at VIM and Emacs.
All of those have their key-combinations to do the things you describe, and you'll simply have to learn them. Moving the cursor around the text, choose formatting, indentation, configure colours for highlighting ans whatnot. But it depends on the editor you choose.
Scripting Godot with GDscript is (arguably) best done with the built-in script editor. The documentation is the right place to start with.
