There's a wonderful book A Midwife's Tale that was pulled from a late 18th century diary of a midwife that might answer some of those questions for you. As for how the average woman found out about these things, it was often much simpler than you would think. Things like childbirth and all that went with it were family affairs. In the diary mentioned she talks about all the women that were in the room during childbirth, the family and community pitched in. Or how many young girls would go to other households to help care for infants during the period just after birth when the mother often couldn't manage to get out of bed, let alone take care of a house. Not just because the other house needed assistance, but to teach the girls how to take care of children and how the process of birth worked, particularly if there weren't young ones at home.

Privacy is a very modern convenience. Sex occurring today in private bedrooms with thick walls and birth occurring in a sterile hospital surrounded by doctors. Some families lived in single rooms. All life began and ended in the bed they slept in every night. And the whole family was in that room for it. The rest, inevitably was up to her mother or sisters to explain.