First, caveat: Centos6 is end of life so you should be upgrading to at least Centos7.
To install epel for a particular distro go to the epel website and that will tell you how to install epel for your particular distribution:
Do not try to mix different versions ie Centos7 / Centos8 as this will cause all sorts ...
You can use yum history to find detailed information about a package installation, upgrade, or removal.
yum history list <package> will give a summary and yum history info <package> will give very detailed information.
[root@vmtest-centos7 ~]# yum history list htop
Loaded plugins: fastestmirror
ID | Command line | ...
The fortune program in CentOS 7, is available under a different package name, fortune-mod, so (with EPEL repo enabled):
yum install fortune-mod
Why it was renamed to -mod is beyond me. But for some consistency of how you install it across different CentOS version, you can actually use binary name in lieu of package name:
yum install /usr/bin/fortune