For attachment of the boot directly to framing:

Confirm the distance from the wall top plate to the boot is per the construction drawings, and mark the distance from the top of the top plate down to the top of the Hanger Bar mounting tab.
Confirm the position of the center of the boot horizontally, and make sure the boot is level and on the measurement marks.
Use two general purpose screws in the mounting holes provided to attach the boot to the framing.
After drywall installation, apply a bead of caulk into the gap between the boot and drywall cut out.