Lay your screen panels down side-by-side. They all should be the same height so the hinges are evenly placed.
Use your ruler to measure the distance from the top of the screen to the place where you want to install the hinge. Mark the place with a pencil.
Place hinges in the marked locations so that they open in the opposite directions from each other. This helps the folding screen to stand up properly.
Drill the holes. Pre-drill a small hole in each hole of the hinge with your power drill deep enough to prepare for the screw only.
Screw the hinges in place. Stand your screen up and arrange it by adjusting the panels.