Dear Nandini,
First you have to decide you want go with firm registration or Pvt. Ltd.
if you want firm then go to the legal department (firm registration office) and get register your company. If you are starting firm in partnership the partners must have partnership deed.
To get firm registration you must have
Firm Address Proof. Like Electricity Bill, Rental agreement etc.
Generally agent will charge Rs.2500 to 3500.
Then you have to apply for company PAN card.
If you have a high vision then turnover more than 10 Lakh then you have to apply for service tax number.
Above are the basic things require to start the business.
Hope above information will help you to start business
Regards