vi is an old style text editor so when you run it, it is in "command mode", i.e. any keys you hit will do something! Good thing is, if you just need to use it infrequently, all you need to know is:
i insert text and ESC to end insert
x delete character
:wq write file and quit
:q quit
u undo!
As said, it is worth learning at least the minimal because no matter what state your system gets into, you know vi will be there!
