Occasionally you may find Vi is the only editor available. To use it to edit somefile.txt type:
This puts you into insert mode and you can type. Type something.
When you are done, type the Esc key to go back to command mode. Type:
(must be upper case) to save the file and quit.
If you don’t want to save, type:
to quit without saving.
At this point I am tempted to add all sorts of other tips, like / to search, but then this would not be a minimalist guide!