the environment varibles are two types system defined and
user defined

system defined are qtp displays by default in environment tab
 where
user defined is two types
Local:we r creating these are in environment tab only for
that test we cant use it to other test

Global: creating in notepad and saving with extension.ini 
what are the environments you need like user name, password,
server name, database these are we can use in any test

Its one and the same thing. In other scripting languages, 
we call global variables and in QTP, its called environment 
variables.