Hi,
Installing webmin is so easy. You only needed to configure the repo with webmin packages and install via yum.
vi /etc/yum.repos.d/webmin.repo
[Webmin]
name=Webmin packages repo
#baseurl=http://download.webmin.com/download/yum
mirrorlist=http://download.webmin.com/download/yum/mirrorlist
enabled=1
x!
Import the key using these steps
wget http://www.webmin.com/jcameron-key.asc
rpm --import jcameron-key.asc
Now
yum install webmin
Open up the port 10000 for webmin.
iptables -I INPUT -p tcp --dport 10000 -j ACCEPT
That is all you needed to do.