Relax, Sarah. When the guest has a confirmed reservation, Airbnb will charge their credit card account and will pay it out to you approximately 24 hours after checkin. Airbnb won't allow someone to book if they don't have enough funds in their account. As for security deposits, Airbnb places a "hold", not a charge, on the guest's credit card in the event there is damage. You have to go through Airbnb to collect money for damages and you have to make a demand within 48 hours of check out. The guest does not pay a security deposit to you outside of these procedures.
You should set up a payout preference right away if you haven't already done so.