When user makes a new booking, I want to take 50% deposit immediately from the guest. I mean if the guest wants to keep his/her reservation he/she must pay 50% deposit. How can we have something like this? Is there some setting in the airbnb dashboard?
If you had read the information for hosts on BnB's website, before deciding to sign up as a host you would have seen that they take payment in full at the time of booking to secure the booking and you receive payment in full within a few days of the guest staying with you.
If you want to operate on a deposit basis - you would be better looking at one of the other rental sites.