Place the gate in the desired mounting position within the gate opening. Place wood blocks under the gate to raise it to the desired height, if necessary.
Position the top hinge so that its mounting holes are over the vertical end and the horizontal top structural members of the gate, if possible. Ensure the mounting holes on the opposite side of the hinge align with a solid vertical fence post. Mark with a pencil the positions of the screw mounting holes in the gate and the fence post. Remove the hinge.
Position and mark the screw mounting holes at the bottom of the gate in the same fashion.
Position a 3/16-inch drill bit installed in a power drill over the pencil marks, and drill pilot holes for the mounting screws into the gate and the fence post.
Position the mounting holes in the hinges to match the drilled holes in the gate. Drive in wood screws using a Phillips bit installed into a power drill.
Lift the gate into position. Use the wood blocks to hold the gate up, if needed. Drive wood screws through the opposite side of the hinge and into the drilled holes in the vertical post with the Phillips bit and drill.
Remove the wood blocks from underneath the gate, if necessary. Swing the gate back and forth to test its operation.