There is nothing called RTI office or head office. Each PA (Govt office) appoints its officers (PIO/APIO) to receive and process requests under RTI (RIGHT TO INFORMATION). A application (with fee) seeking copy of documents/information becomes RTI application. Payment of RTI fee and format of the application has to be as per the rules of the authority (Govt office). Please read: WHICH RULES TO FOLLOW? - RTI Guide
To acquaint yourself with RTI please go through the 'All About RTI' links on the homepage and the RTI Guide (RTI Guide) section of this portal.
If you have any specific query please post it in the relevant section.