Enroll at college as an English literature major. While this may not be the most affordable or convenient option, a literature degree offers the most comprehensive study of literature available. English literature graduates are expert readers of literature. Some community colleges offer "Introduction to Literature" courses at night. This is a good option if you just want to get a taste for the academic study of literature without committing to several years of study.
Sign up for a library card at your local library. You can borrow literature for free, including literary anthologies that college students typically study. These contain collections of the most significant literary contributions over the centuries.
Read a book from the library or a bookstore that presents a survey of the top 50 or 100 works of literature of all time. This is a good place to begin your study of literature. Often, the author of these literature survey books will provide a brief description of each novel or poem so that you can not only learn about the background to the novel and what themes it discusses, but find out what books interest you.
Find a copy of a literature guidebook, such as those by Coles Notes or SparkNotes. These books include chapter summaries, discussions of themes, motifs and symbols, historical context, discussion questions and suggested essay assignments. Guidebooks like these can help you make sense of a work of literature and understand its significance in the literary canon.