The key bindings in this mode is the same as in the emacs mode except for
the following 4 keys. So, you can move around in the buffer and change
its content while you are in insert mode.
<ESC>
This key will take you back to vi mode.
C-h
Delete previous character.
C-w
Delete previous word.
C-z
Typing this key has the same effect as typing <ESC> in emacs mode.
Thus typing C-z x in insert mode will have the same effect as typing
ESC x in emacs mode.