How do you edit files with vi? I know this might be a vague question
but try your best with the default and most common answers.

the most basic commands for using vi are:

open the file at the prompt.

vi filename

then vi opens. 

move the cursor to where you want to edit with the arrow keys.

push the 'a' key for insert.

now you can type whatever you want.  when you are done push the escape
key to get out of the editing mode.

now you can move around again with your arrow keys.

if you want to save what you have done type  :wq  (yes include the : also!)

if you want to quit without saving type    :q!   (yes include the : also!)

there are alot of help pages online about this, just google "vi commands"