ABAP is a programming language and it is not that different compared to other programming languages so you can apply all the processes you usually use to develop a software product. The only difference is installing ABAP code at a customer system because you cannot just copy a bunch of textfiles onto a cd and then send it to the customer. You will need to download a so called transport request or use saplink. A tool which allows to move code from one system to another. Check their website here: http://code.google.com/p/saplink/
By the way please ask more specific questions. People in this forums have only a limited amount of time and are not getting paid for answering questions so make it as easy as possible for them.
cheers
Thomas
