For detail click on this link to get all the detail about rules of reservation - http://www.indianrail.gov.in/reservation_Rules.html
Yes, you can. In fact, you can book your ticket for any train on the Indian Railways network, from any originating station to any destination* at any of the Computerized Reservation Centre’s, across the country. With the networking of New Delhi, Mumbai, Kolkata, Secunderabad and Chennai Passenger Reservation Systems, you can now book your onward and return journey tickets from any computerized Reservation Centre nearest to you – not just from major railway stations. This networking makes reservation of tickets faster and simpler.
* Reservations can be made subject to distance restrictions and availability of quotas.
You can reserve your ticket 120 days in advance, excluding the date of journey at the train Originating station. At intermediate stations where the train arrives the following day, Reservation can be done 120 days in advance. In the case of some intercity day express trains, the advance reservation period is less.
The reservation status will be clearly indicated in your ticket. If your ticket is confirmed, your coach and berth numbers will be mentioned on your ticket in all classes other than First Class and AC First Class. For these, the word “Confirmed” will be printed alongside the class of travel. If your ticket is in RAC (Reservation against Cancellation)/Waitlisted status, the same will be mentioned on the ticket.
You can board the train with an RAC ticket. You will be provided with sitting accommodation initially and allotted a berth (in case of passengers not turning up) in the train.
If you don’t have any ticket, you may approach the Train Superintendent/TTE after purchasing an unreserved ticket from the booking office. The TTE will allot the accommodation, subject to availability.
You can contact the Enquiry Counters at your nearest Computerized Reservation Centre or call 139 from your mobile, landline phone to The Interactive Voice Response System, available at major stations. Remember to always quote the 10 digit PNR Number indicated on the upper left hand corner of your ticket, to find out the current status. The current status of your ticket can also be obtained from the following http://www.indianrail.gov.in/pnr_Enq.html
The railway telephone enquiry system is automated telephone enquiry system, which gives you details of accommodation availability and the current status of your tickets. Dial 139 from any mobile, landline phone of any network to get detail.