After you book ticket with Air India, either online or offline, you are given a PNR number. Using this number, you are able to access all the information relating to travel itinerary. You are able to see the status of booking.
It shall be noted that the PNR numbers are also generated by the online travel agencies. If you have got the tickets booked from an online agency, then the PNR number will be their own and will not fetch you details from the Air India website. In that case, you shall have the e-ticket number which only airlines issue and quote the same to the airline if the status is to be checked with the airline. Else, you can always seek this status information from the agency which booked ticket.
You can use the PNR number for modifications of travel itinerary by visiting this link https://book.airindia.in/itd/itd/lang/en/reservations and filling the required information, as show below.
You are required to quote this number every time you have queries relating to any service of the airline, such as allowances, addition or redemption of frequent flyer miles, online check in, ticket cancellations, refunds requests and status and many others.