What is ADS(active directory service)?
What are the functions of it?
Why it is used?
What is the use of this?

What is the purpose of configuring ADS on my server?
How to configure ADS?
ADS is also need to configure on local host machine.

Guide...

Your questions are too broad to answer here. Your best bet is to either take a course on the subject or get a book: Amazon.com: active directory: Books (http://www.amazon.com/s/ref=nb_ss_gw?url=search-alias%3Dstripbooks&field-keywords=active+directory&x=0&y=0)

AD is primarily a security model for all of your users, computers and other objects within your network. This could include email as well. It is a very broad subject that can take many weeks of intensive day long classes on the subject.