I would normally take time to discuss each chapter of the book in detail. However, this book does not lend itself to this process. It is a single unit expressing love for the opposite sex. It does have a myriad of metaphors, oriental symbolism, and many interpretation problems. For the purpose of these posts, I will use lecture notes from my class on marriage setting the book in six themes. The notes are adapted and taken from One Plus One (Endemano, Rice, Gibbs & Berry, 1996).
I will attempt to provide a brief explanation of the book and its possible interpretations. Some see it as an allegory because they do not believe that God would include such a sexual oriented story in the Bible. With this perspective, sex seems bad even within the context of marriage where God applauds the act (Hebrews 13.4). The most common allegorical interpretation is that Christ is the bridegroom and the church is the bride which follows New Testament symbolism. This is acceptable except for the question, what did those before Christ do with the book?
Some view it as typology, which is similar to allegorical but with added thought that the story itself is real with a real bridegroom and bride. This view, like the allegorical, holds that the only real meaning is found in finding the spiritual meaning behind everything. The danger of course is found as the reader reads too much into each element of the story.
Others view the story as literal, which takes the book as it is written. There was and actual couple whose story is told in these eight chapters. Like any good story it uses metaphors and symbolism along with euphemisms to relay the story.
Some combine the views giving the story an actual historical setting that prefigures the love Christ will display to His bride, the church.