Drywall panels cover wall and ceiling surfaces, resulting in smooth finish. The panels are cut to size and screwed to the wall studs or ceiling joists. However, holes must be cut for lights, electrical sockets or air conditioning vents. Otherwise, the drywall will not sit flush with the studs. The holes can be cut with a manually-operated drywall saw, but the job is faster if a rotary cutting tool is used instead.
Measure the center-to-center distance between the wall studs. Most walls are constructed with 16-inch centers. A typical four-foot wide sheet of drywall should span across four studs; one on each end and two in the middle.
Draw vertical lines on the sheet of drywall every 16-inches with a pencil and four-foot level. The lines correspond to the stud spacing you measured in the previous step. If the stud spacing is different, use that spacing to mark the drywall.
Measure the wall from floor to ceiling to determine the wall's height. Measure and mark a horizontal line across the top of the sheet of drywall to this same measurement.
Score the horizontal line with a utility knife. Snap the drywall at the scored line and fold the excess material approximately 90 degrees. Cut the paper along the crease on the back side of the snapped line and remove the excess material. The drywall sheet is now cut to size.
Measure vertically from the floor to the center of the air conditioning duct in the wall. Measure horizontally from an adjacent wall to the center of the air conditioning duct. Transfer these measurements to the sheet of drywall with a tape measure and mark an X where these two measurements coincide.
Place the drywall sheet against the wall. Do not push too hard, as the flanges of the air conditioning duct (or electrical box) may damage the the drywall.
Turn on the rotary cutting tool and plunge the bit into the center of the X mark. Move the tool up until you feel the bit contact the inside of the air conditioning duct's flange. Move the tool around, following the inside of the duct's opening until the drywall has been cut away. The inside of the duct should now be visible, but the duct's flange is still pressing against the back of the drywall.
Plunge the bit into the drywall approximately 1/8th-inch past the opening you just cut out. This puts the bit on the back side of the duct's flange. Move the tool around the perimeter of the duct. The bit should ride around the outside of the duct's flange.
Push the drywall against the studs. The duct's flange should fit snugly inside the opening you just cut. Screw the drywall to the studs using drywall screws and a drywall screw gun. Install a screw approximately every eight inches along each vertical line you drew in Step 2.