Try Voltaire's "Candide." It's a really easy read, you can probably do it in about a day. As you read, think about what institutions of Old Regime France Voltaire targets with his satire, how and why he satirizes them, and what you can learn about his attitudes towards various aspects of society. The novel addresses various features of not just French society but mainland Europe and colonial issues as well. I recommend the edition translated by Helena Rosenblatt because it includes a really good foreword to give you some context.

Ideally, you won't need to read anything before hand. Providing that this is a university class and your professor is having you read enlightenment thought, it won't be that much. However more likely you'll be focusing on the earlier Enlightenment thought like Spinoza's Ethics or Leviathan by Thomas Hobbes, perhaps Decartes' Meditations.

Later Enlightenment philosophers didn't really focus much on religion as they were more focused on the role of government and the people (such as John Locke's Second Treatise on Government and Rousseau's Social Contract or even Adam Smith's On the Wealth of Nations). Again, ideally you shouldn't need to read anything outside of your class as your professor should have it included in your book list, however if you want to pull a Hermione Granger, read those and anything by Jonathan Israel, a good Enlightenment historian that has written a trilogy of series histories on the Enlightenment but might be a bit much for you.

If you have more questions, ask away but I bid you good luck.

From late in the Enlightenment, Thomas Paine's Age of Reason and Jefferson's Bible.

Ben Franklin's writings on religion are exceptional, in that he comes across neither as a believer nor as a critic of religion, but as one who takes up the challenge of trying to develop his own beliefs relying on his own intellect.