How to give administrative previledges

[Chethiya K Ranaweera]

Hello people,
I want to create a user with administrative peviledges. First I
created a user and checked the /etc/passwd file. His IUD and GID were
500:500( I think this is by default from Redhat). Then I tried to
change GID to 0, logged back into the system. He did not have admin
access. Does anybody know how to give a user administrative
previledges, so that he can update the system ,,, etc??
 
-Chethiya