The Bhagavatam, also called Bhagavata Purana, is Vyasa’s last Purana.
Bhagavan, the Lord, is Krishna, whose life is told in the tenth of twelve chapters (Cantos) with around 4,000 verses. In total, the work has around 18,000 verses.
Vyasa’s son, Shuka, narrated it to King Parikshit during the seven days he waited for his death. Even today it is considered auspicious to read the Bhagavatam in seven days.
Since this is impossible, abridged Bhagavatams were written, one of them is the Narayaniyam, composed by Narayana Bhattathiri.
Read how Bhagavatam was written
http://hindumythologyforgennext.blogspot.com/2013/01/how-was-bhagawat-puranam-written.html
Read Bhagavata Purana
https://archive.org/details/BhagavataPuranaMotilalEnglish/mode/2up
Read an elaborate summary
http://sushmajee.com/bhagvatjee/index-bhaagvat.htm
Read Narayaniyam
http://narayaneeyamtrans.blogspot.com