I don't understand what it means. 

This novel simply doesn't make any sense.

This book was boring and useless.

If you've ever felt this way about a work of literature, maybe the time has come for you to learn a few tricks readers employ when they are grappling with a difficult book. Or just any book. 

Books, like onions, can make us cry... no I didn't mean that analogy (even though it's sometimes true) I meant that books, like onions, have layers and the more layers you find, the more enjoyable a book becomes. The more layers a book has, the longer it stays with us after we've finished reading it. The more layers you discover, the deeper your understanding of the world will be. Because books are not just like onions, they are also like windows on the world...

So let's learn how to open those windows and how to peel those onions, possibily without any tears....