It's a redhat updater.... kind of like Windows Update.... you can use it to install and update packages from RedHat or any other party that compiles it as a YUM package. SuSE call it YAST(2).... it's just an updater that makes things easy.
Easiest way to install mySQL is to use what's there (YUM).... however you can always download and install manually by following the guide over at mysql.com....
YUM seems to be more of a Fedora Core thing, but RedHat should have some type of software managment tool to update/install new items easily (if you're using a GUI); otherwise, you're down to doing it manually....