Yum

YUM, it's not just good eatin', it's also for updating your RedHat (or CentOS) packages. https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/ch-yum.html

What are the top 20 yummiest commands? http://www.tecmint.com/20-linux-yum-yellowdog-updater-modified-commands-for-package-mangement/

Sometimes, you want to use a new repository. Like when installing Jenkins (although it's found in the regular repos, so maybe this isn't the best example for needing a separate repo)

from http://pkg.jenkins-ci.org/redhat/

sudo wget -O /etc/yum.repos.d/jenkins.repo http://pkg.jenkins-ci.org/redhat/jenkins.repo
sudo rpm --import http://pkg.jenkins-ci.org/redhat/jenkins-ci.org.key
sudo yum install jenkins