Position the battens placing two about 12" from the ends of the boards for tall shutters like these. If your shutters are shorter, you may want the battens slightly closer to the ends. Position the third batten so it is centered on the length of the boards.
Now place the boards on the battens, making sure that the ends are aligned.
Then drive screws through the boards and into the battens from the back.
Finally, prime and paint the shutters the color of your choice.