What's a Patch?
 

What is a Patch?

you will find your answer here:
http://www.megagames.com/psx/psx_patches.htm

How to make Patches file
 

Your link was helpful. It gave me a better understanding about Patching. I thank you. I notice there are a long list of Patches on the page you refered me to. Can you also tell or refer me to a site that will help me create a Patches file for a particular game? (say Resident Evil 3 US Version or Crash Bandicoot US Version)

Well this is a good place to start looking....

http://www.paradogs.com

But unless you are seriously thinking about getting into coding in a big way then i would suggest that you give up before you start.

Have a look and decide for yourself.