yum search your_package_name (will tell you if the package is installed)
yum install your_package_name
yum remove your_package_name
yum update (will update your system)
yum -y update (will totally automate your update)
From the Linux.Duke.edu site:
Yellow dog Updater, Modified
Yum is an automatic updater and package installer/remover for rpm systems. It automatically computes dependencies and figures out what things should occur to install packages. It makes it easier to maintain groups of machines without having to manually update each one using rpm.