How do I add the elrepo repository to my linux computer?

Assuming you have root, follow the below steps.
  1. # rpm --import http://elrepo.org/RPM-GPG-KEY-elrepo.org
  2. For CentOS6:
  3. # rpm -Uvh http://elrepo.org/elrepo-release-6-5.el6.elrepo.noarch.rpm
  4. Add relevant priority-flag to the repo in /etc/yum.repos.d/.