Open the hinge. You should see a ridge running down one side of the body; this side will be referred to as the top of the hinge.
Align the hinge with one edge of the box, with the top up. Make certain that it's straight, and attach it to the box using a wood screw at both ends. Fill in the remaining holes with screws so that the hinge is firmly attached to the box.
Align the underside of the lid with the hinge. The lid should butt up against the box if the hinge is opened flat. Attach the hinge to the lid with a screw at both ends, and fill in the remaining holes with more wood screws.