What is virtual applience?

To cut it in short its a stripped down version of Operating system designed to perform specific jobs.

To get more details please refer.
http://download3.vmware.com/media/vam/vam_demo.html

what is EPEL ?

https://blogs.oracle.com/OTNGarage/entry/pimp_my_ride_installing_additional

Sudo Learning.

http://www.unix.com/shell-programming-scripting/177264-need-some-expert-advise-running-scripts.html#post302604691