There's a review of a book by Edward Paice in the Telegraph that gives some useful background to Candide.
The book is about the Lisbon Earthquake of 1755 and the reviewer discusses the effect this major disaster had on Voltaire. In Candide, Candide's tutor, Dr Pangloss, keeps repeating Leibniz's view that everything is "for the best in the best of all possible worlds".
If you click HERE you'll find a link to a translation of some lines from Voltaire's poem on the Lisbon earthquake. You can find the text in French with Voltaire's preface (also in French) HERE.