`nano` - a small and friendly text editor

nano [file]

Gotchas

^O write out, ^X exit, ^K cut a line, ^U paste, ^W search, ^\ replace. ^ means Ctrl.
Editing a root-owned file needs sudo nano - otherwise the save fails at the very end, after you typed everything.

Try nano in a real terminal Free, in your browser - a real Ubuntu terminal to try it in, with missions that check your work.