Infrastructure Software

When installing OL 6-3 I am asked to specify the root user and at the end of the installation a non admin system user.

I am slightly confused as to the purpose of this non admin system user.

Q1. What is if for / not for and how does it differ from root ?

Q2. Is is really just the Desktop Admin user ( whereas root is the superuser for the server as a whole ) ?

Q3. Now that I have specified this non admin user - how do I change this role to another user I have created ( I made a poor choice of username in the first place ! ) i.e. does this non system admin user have any specially designated roles or privileges at Linux level, which I need to enable on the other user that I now wish to be the non admin system user ?

Advice greatly appreciated,
Jim