If you go to the Goodreads sign in page, they’ll tell you that they have two main, laudable goals. They help you find more books that you might like to read, based on your past reading history (which you provide). And they help you connect to other readers who like to read similar works.
With over a million unique visitors every day, Goodreads is a valuable tool for writers, both for its stated purposes (because writers are also readers), and also because Goodreads connects them with readers. Here’s some ideas to get you started using this site.