Split the screen in vi - horitzontally or vertically

Most of us have some time in need to compare the two files to compare same file on different line or section,

then you will find 'split' can be very handy.

 the simplest usage is to type 'split' command that will split the screen horizontally.
:split

You can split the open file the open file in vi  vertically by
:vsplit

to switch between the screen you need to use
cntrl+ww

To unsplit/ close the open file , you need to use simple command
:q!