SUB is a method
FUNCTION is to return a value to it

sub does not return's a value,but function return's value

Function always returns a value but sub does not.

Sub keyword is used for the procedures and procedures never 
return a value where function key word is used for function 
and function returns a value that can be assign to any 
variable.

Function returns a value, Sub doesn't.
Function can be called from within a cell, similar to
=Today() function.

sub does not returns a value but function returns a value