Right.
So you got the lock cylinders when you bought the bike, as we all did. And your FOB has a mechanical key blade. You'll see that the lock cylinders are presently encased in a black plastic pipe which will enable you to insert them into the pannier's lock receptacles. A number of pins in each cylinder are displaced by the insertion of your unique key.
The process is not hard, in fact it is rather rewarding if you haven't keyed a lock before. But you have to stay on point and focus or you'll mess it up.