After hearing about the creation of Brahma in the previous chapter, culminating with the creation of the Manus, Vidura asks to hear more about the descendants of Svāyambhuva Manu.
Most of the narrations of the Srimad Bhagavatam revolve around the genealogical tree that started with Brahma and his sons. This succession started at the beginning of the current day, with the creation of the universe, and continues up to now. The genealogical tree of every human being, as well as every demigod or demon, can be traced back to these original personalities who have existed since the beginning of the universe.
We can see that although it is declared right in the first verses that the Srimad Bhagavatam deals only with pure topics connected with devotional service to the Lord and all forms of fruitive activities and materialistic religion are rejected (dharmaḥ projjhita-kaitavo ’tra), there is a lot of discussion about family life. In chapter 21 we will study the conversation between Manu and Kardama Muni, where Manu convinces him to accept his daughter Devahuti in marriage, in chapter 22 we hear about their marriage, in chapter 23 about their honeymoon, including details about their sexual life, and so on.
Srimad Bhagavatam #29: Kardama Muni and Devahuti