One or more existing officers in every Government Department have been designated as Public Information Officers (PIO). These PIOs act like nodal officers. You have to file your applications with them. They are responsible for collecting information sought by you from various wings of that Department and providing that information to you. In addition, several officers have been appointed as Assistant Public Information Officers (APIOs). Their job is only to accept applications from the public and forward it to the right PIO.
submit application as:
You can do that with the PIO or with APIO. In the case of all Central Government Departments, 629 post offices have been designated as APIOs. This means that you can go to any of these post offices and submit your fee and application at the RTI counter in these post offices. They will issue you a receipt and acknowledgement and it is the responsibility of that post office to deliver it to the right PIO. The list of these post offices is given at http://www.indiapost.gov.in/rtimanual16a.html