Lay the door to your Ikea furniture item on a flat working surface with the door front facing downward. You should have access to the pre-cut hinge holes on the inside of the door.
Insert the rounded end of an Ikea European Pax hinge into the cutout in the door. The long, bar end of the hinge should hang over the edge of the door and onto the floor. Line up the screw holes in the rounded end of the hinge with the screw holes at each side of the hinge cutout. Use your Phillips screwdriver to tighten the screws provided so the hinge is firmly in place. Repeat the process for the second and third hinges as needed.
Hold the door up to the assembled cabinet, at the door opening. Line up the screw holes on the edges of each hinge with the corresponding set of screw holes on the inside of the cabinet. Use your screwdriver to tighten the screws provided for each hinge. The door should now hang from the cabinet on its own. Open and close the door to test the hinges.