HI Afsarul, twin sharing mean that the accommodation you will sharing will be shared by someone else. I'm not sure what are you asking to pay here, if you have redeemed a free trip you don't have to pay anything.
Bro, it means you have to share your hotel room with co-traveller. But I guess it will be fun, you will get lots of experience from roommate and get a buddy for another trips. It will help you to grow community