Stand in the doorway and reach your arms up as far as they'll go; use a pencil or piece of tape to mark the doorway about an inch below the heel of your hand on one side. Place a mark at the same level on the other side of the doorway, by extending a 3- or 4-foot level across the doorway, or by measuring up from the floor.
Center the chinning bar's holders over the marks you made and, with a pencil, mark the location for its three screw holes.
Remove the holders and drill a pilot hole for each screw. If you don't have a drill or the correct size drill bit, pound a nail partway into the wall at each mark, then remove it, to create a pilot hole. The nail should be slightly thinner than the screw shank.
Place the holders back and screw them into place.
Repeat the same procedure for the second set of holders. Mount these a little higher or lower to accommodate a second user of a different height for pullups, or mount them a few inches off the floor to use as an anchor for situps.
Twist the end of the bar counterclockwise to lengthen it until it sits firmly in the mounting cups, pressing against the doorway on the other side.
Open the door and stand on the side of the threshold farthest from the door.
Hold the multi-function bar in your hands as if you were doing pullups. Poke the far end of the multi-function bar, which curves upward, through the doorway. The actual pullup handles should stay on your side of the doorway.
Position the up-curved end of the multi-function bar atop the doorjamb on the far side of the door, then lower the pullup handles on your side of the door to wedge the multi-function pullup bar into place. Step through the doorway to verify that the up-curved end is fully seated, tight against the wall and flush with the top of the doorjamb. Always verify that the pullup bar is properly positioned before every use.