@saifuddin9122 - Can you please provide more context and information? Like what are you referring to when you say "it"? The more information you provide to the Answers community, the better chance that someone will be able to help you.
It's not so fully clear your question, do you want to know what are role and functions of Search Head in Distributed Splunk architecture?
If this is your need, You could find in Splunk documentation site many useful information
there is also an eLearning free course that describes Splunk architecture http://www.splunk.com/view/SP-CAAAHSJ
The search head:
Let's users search against indexed data Controls Summary Indices Can be the Monitoring Console Can be the Deployment Server Can be an Indexer (all-in-one architecture)