Measure the height from the ceiling from the floor where you are going to hang drywall.
Cut the 12-foot length of 2-by-4 lumber to the the ceiling height measurement obtained in Step 1. Keep the scrap lumber for the next step.
Hold the two pieces of 2-by-4 lumber square by using a carpenter's speed square, making what will look like a uppercase T with the two pieces.
Fasten the two pieces square with your choice of nails or coarse-thread screws, using a hammer or electric screwdriver.
Lift a sheet of drywall onto the top of the T-shaped jacks and fit it into place on the ceiling. While using the T jacks to hold the drywall, you should be ready with drywall screws and a drill with screw attachment or electric screwdriver to immediately fasten the drywall to the ceiling. This will keep the drywall sheet in place and keep it from falling or popping out of position.