The document outlines 20 hidden or lesser-known features of popular social media platforms like Facebook, Twitter, LinkedIn, and Pinterest. Some of the featured tips include saving links and articles to access later on Facebook, replacing ads with baby animal pictures on Facebook using a Chrome extension, embedding SlideShare presentations directly into tweets, and creating a photo collage directly in a single tweet on Twitter. The document also provides tips for adding hidden relationship notes on LinkedIn profiles and using trackable links on Pinterest that won't get flagged as spam.