Lester & Helen,
Your third item answers the first! Your white plastic thingy is a 'tacker' that you rig around your furled headsail, and to which you attach the tack of your gennaker with a quick release snap shackle: you also attach your downhaul to the tacker, and run the downhaul down to a block on a shackle affixed to the forward end of your deck forestay tang; and lead the downhaul then aft to one of your bow cleats.
Try setting your tacker about five feet above the deck to start: will depend on your luff length and sailing angle as to the best height for the tacker to be set. The point of the tacker is to keep the tack inboard on the centerline. When snuffing, release the quick release snap shackle to 'blow' the tack, and then snuff the sail with the sock.
Re your second item: the sheets go aft to those turning blocks which I hope then give you a fair lead to your primary winch.
Have fun with your gennaker!
John Knight
Larking About IP40 Rock Hall FOR SALE!
Adventuress IP 420 Brunswick GA about to leave to head north.