Forums / Cotonti / Support / Using $tab

Tell me please how to work with '$tab' function.I need it to work in users.***
I'w tried to just simply surround the needed part of the code with if($tab=='basic') {...} and use the link 'users.php?m=details&tab=basic' and 'users.php?m=details&id=1&u=SunChase&tab=basic' but it just doesnt show anything.