Apply a generous bead of silicone sealant on the inside surface of the nail fin on either side of the window. Lift the window up and into the rough opening, taking care to protect the wood veneer on the head, seat, and side boards of the unit. Provide temporary support underneath the window until the cable system (provided) or other permanent supports are installed.
Check the level of the window at the seatboard parallel to the wall and shim under the unit as necessary. Next use a jack to lift the outside edge of the window as shown so that it is approximately ¼” above level. DO NOT remove the jack or temporary supports until the window is permanently supported.