Close the gate so the gate is flush with the gate post. Hold a ruler horizontally and position it against the gate and gate post at the height you intend to install the latch. Use a pencil to scribe a horizontal line across the gate post and vertical portion of the gate frame.
Test fit the latch and catch on the gate and gate post. Position the baseplate and striker bar an the gate, centered vertically to the scribed line. Position the catch, including the pivoting arm and baseplate, on the gate post, centered vertically to the line on the gate. Position the latch and catch so the center of the horizontal portion of the striker bar is centered to the pivoting arm in the catch. Pass the tip of a pencil through each screw hole in the base plates to mark their positions of the gate and gate post. Remove the latch and catch.
Drill a pilot hole through each screw-hole mark. Position the catch on the gate post, aligning the screw holes in its base plate to the pilot holes in the gate post. Use a drill and driving bit to screw the catch to the gate post with one screw in each screw hole.
Position the latch, including the base plate and striker bar on the gate, aligning the screw holes in its base plate to the pilot holes in the gate. Use a drill and driving bit to screw the latch to the gate post with one screw in each screw hole.