Insert
mode: In this mode you can enter or modify text. To enter
this mode you must use an insert command such as i,
o, or a.
To exit entry mode you should use the ESC key.
Command
mode: In this mode you do such things as move to a specific
line of text or a letter in a line by entering positioning commands.
This is the default mode in vi so there is no special command
to get to it.
Ex mode:
This mode allows you to execute advanced editing commands such
as saving everything from the buffer to disk or erasing all changes.
To get to this mode use the :
command.
