Relays
Swami, if you are good with designing hardwire relay systems, you have the best fundamental base a person could have. A lot of people, including myself aren't efficient at troubleshooting complex "older" relay systems, we just don't work them on a daily basis.
A good place to start, is obviously the tutorial on this site. Then go to manufacturers websites and download manuals for the PLC/HMI components. Commonly they have sample programs in the manuals, which are typically downloadable PDF files and are usually pretty easy to understand.
Good luck!
Greg