You are only allowed to ask one question at time so I edited down accordingly. You can post your other questions separately.
Norethisterone is a member of the progestagen family. The progestagens are a group of steroid hormones that are involved with pregnancy and menstrual cycles in women. They all are composed of four different carbocyclic rings fused together (3 six membered rings and a five membered ring). Norethisterone is specifically used for menstrual cycles. Specific applications include the treatment of PMS, irregular menstrual cycles, and menopausal symptoms. Interestingly, it was the first progestagen to be synthesized in a lab and was used originally among the very first oral contraceptives. Man-made pregestagens are also called progestins.