Place the two pieces of lumber together in their closed configuration.
Position the hinge over the two pieces of lumber with the hinge folded open completely. Remember that the lumber will split apart on the side opposite where the hinge is located.
Drill holes through the lumber to coordinate with the holes in the hinges.
Screw in the wood screws to secure the hinge in place.
Test the hinge to ensure it folds properly. Two pieces of lumber will not fold tight against each other when the hinge is closed.