Steps to Book your Nano online

Book online:

1.The cost of the Online Form is Rs. 200/-. Fill out the application form online and proceed to make an online payment.

2.Your application will then be directed to a third party payment gateway site

3.You will then submit your payment through net banking.

4.The amount to be paid is the Cost of Application Form plus the Booking Amount.

5. The site will confirm your payment by generating a transaction ID.

6.You will be then guided back to the Tata Nano website where a Unique Identification Number (UIN) will be generated.

7. you can take a print of receipt

8. an email is sent to you with the receipt Filling of Application form

For details check these sites
Source
Book-Online