The frame pieces hold the board together and prevent the pieces from moving after the board is in place. Before building the island, assemble the frame by matching the numbers at the ends of the 6 larger frame pieces together.
Using your 19 terrain hexes, you can then construct the island of Catan as shown in the rules for your earlier version.
The frame has fixed harbor types. To vary the harbor types, take the 9 harbor pieces and randomly place them on top of each harbor on the frame.