For a bulletin board, start by making 5 or so missions you would want. Once those are all made, make an event that looks like a sign/bulletin board, and have the first line set a variable called 'Random number' to a random number between 1 and 5. Conditional branch it (Or fork conditions, whatever you XP people call it
), and say if Random number is 1, display the first mission. If Random number is 2, display the second, and so on.
If you want more than 1 job available, instead of putting out one mission at a time, say if Random number is 1, show choices of 3 or so missions.
^^ Hopefully I made sense.