It's pretty simple: log in through the portal, link your BluChip ID, browse and pay for duty-free goodies online before your trip, then pick them up at the airport.
Your rewards are credited within 24-48 hours of completing the purchase.

Right now, you can use this at Mumbai, Ahmedabad, Thiruvananthapuram, Jaipur, Mangaluru, and Lucknow airports.
Guwahati and Navi Mumbai International Airport are joining soon, so more chances to earn while you travel!