Need help for setting up yum

Hi all:

I have issue with yum update, when I type "yum install http" I got follow info:

# yum install http
Loaded plugins: refresh-packagekit, rhnplugin
This system is not registered with RHN.
RHN support will be disabled.
Setting up Install Process
No package http available.
Error: Nothing to do

so how to registered my Redhat?