These are two poems and one is most definitely longer than the other. But before I go any further I should say that I was blown away by how much I enjoyed reading them. As you have probably worked out, I find poetry difficult to read and so it is not my natural choice. But even though I was worried that the language would make the experience even worse I loved them.
So Paradise Lost is the first and longest poem and is all about the fall of Satan from heaven and his new plan to get revenge by spoiling God's creation of mankind. It's like an extended version of Genesis 3 and right at the end you get an overview of all that happens in the Old Testament. There are parts that are not biblical, probably, but I think it is a great way to understand what happened back in the Garden of Eden.
The second poem is, as I'm sure you have guessed, Paradise Regained. It's all about Satan's temptation of Jesus and his plot to stop Jesus from carrying out His rescue. I liked it less, to me it felt less credible than Paradise Lost but I think it still does a good job of bringing to life an important part of God's plan for salvation. Would highly recommend both of these poems. It should be on your book bucket list!