Milton's Paradise Lost is an example of Puritan literature primarily because it celebrates the sanctity of life.
Paradise Lost is about Adam and Eve—how they came to be created and how they came to lose their place in the Garden of Eden, also called Paradise.
It's the same story you find in the first pages of Genesis, expanded by Milton into a very long, detailed, narrative poem.
It also includes the story of the origin of Satan. Originally, he was called Lucifer, an angel in heaven who led his followers in a war against God, and was ultimately sent with them to hell. Thirst for revenge led him to cause man's downfall by turning into a serpent and tempting Eve to eat the forbidden fruit. - ParadiseLost.org
For chapter summaries and explanations, see SparkNotes' Paradise Lost Study Guide.