What you are referring to is a Next Cruise. FCC is a future cruise credit that is issued for cancellations.
A next cruise credit allows you to book a cruise for $100pp deposit (Junior suites and below, full deposit for GS and above). This is also a non refundable deposit booking.
You will get an On Board Credit based on the cabin type and sailing length (7 day sailing in a balcony is a $100 OBC...total, not per person). You do not have to pick a ship and sail date immediately but if you do not choose one within 2 months you will lose the OBC and if you don't pick one within 12 months you lose your deposit.