Hi, welcome to oVirt community!

I understand you're trying to install oVirt for the first time.

I guess you already started reading oVirt Install Guide and following http://www.ovirt.org/documentation/install-guide/chap-Installing_oVirt/ you  tried to install ovirt-engine without having enabled the ovirt repositories.

Please read http://www.ovirt.org/download/ before starting the oVirt installation, it will explain how to get all needed repositories in place before starting to install it.

I'm also assuming you're trying to run yum on a supported platform. Please check supported platforms on http://www.ovirt.org/download/ 

If you need help, you can find us also on IRC, see http://www.ovirt.org/community/