How do I write the COBOL mainframe coding?

Answer 1

I'm not sure I understand the question. If you're wanting to know in general terms how to code a COBOL program, you create the source code in some manner (most likely in a text file, as I doubt you have a 60s-era card punch sitting around with a card reader to process the deck) and then pass the source code to a compiler to (assuming no syntax errors) create an executable.