access global variable of drupal into another php files

I want to access global variable of drupal (like user variable in
drupal) into another php files
I Create a new module for example test module.
my test module have 3 files . test.info , test.module , main.php
I want to use global variable of drupal into main.php as following code

global $user;
please guide me how can i access this drupal variable in my page?
thanks