Sandeep,
A non SAP example, we have different pair of shoes for different purposes, sports shoes when we go out for a run or to play, leather shoes to wear to office, etc. etc. Similarly for different SD business processes, we use different sales document types.
Search the internet, check IDES, VOV8, fields like sales document category etc. and you will get lot of information.
TW
Internet has a vast amount of information, for probably ALL SD related questions.
Added - Get TSCM60 and 62 these are SAP study material for certification exam. These are great study material.
Before answering your question, I had a quick read of the relevant chapter in TSCM60.
Message was edited by: TW Typewriter