Explane how do mammals reproduct

*well, most of the mammals are viviparous, giving birth to live young, besides such species of monotreme as the platypuses and the echidnass still lay eggs. Mammals differ into three types: monotremes, placentals and marsupials, all with internal fertilization. In placental mammals offspring are born as the complete animals with the sex organs present though not yet functional. After some period of time the sex organs develop to maturity so these animals become sexually mature. Most of the female mammals are only fertile during certain periods during their estrous cycle, which is when they're ready to mate. Individual male and female mammals meet and carry out copulation. Most of the mammal types exchange their partners thoughout their adolescence. Do you need the detailed answer about their reproductive systems and difference from other types of animals or this fairytale will be enough?