What do estrogen and progesterone do?

Inner lining: Estrogens produced by the ovaries during the first half of the menstrual cycle, before ovulation, make the inner lining of the uterus grow to provide a nice cushion for a fertilized egg. After ovulation the ovaries start producing progesterone which transforms the inner lining into that nice cushion. When there is no pregnancy, both hormone levels drop at the end of the cycle and menses commence.