Find out what version you're running
cat /etc/redhat-release
find out if 64- or 32-bit
uname -m
install with yum
yum install
uninstall with yum
yum remove
remove or delete a file
rm
installing RHEL EPEL repo
https://www.rackspace.com/knowledge_center/article/installing-rhel-epel-repo-on-centos-5x-or-6x
more yum stuff:
https://www.cyberciti.biz/faq/rhel-centos-fedora-linux-yum-command-howto/
 
weird "issues" (aka n00b mistakes)

warning: epel-release-6-5.noarch.rpm: Header V3 RSA/SHA256 signature: NOKEY, key ID 0608b895
error: Failed dependencies:
    rpmlib(FileDigests) <= 4.6.0-1 is needed by epel-release-6-5.noarch
    rpmlib(PayloadIsXz) <= 5.2-1 is needed by epel-release-6-5.noarch

Installing for wrong version! (see above to check your version)