LinkedIn is a professional networking platform with over 100 million members that can be used as a tool to build business referrals through relationship building. The document provides tips for using LinkedIn such as growing your network through helpfulness and quality over quantity, moving relationships offline, following up well, promoting others, expressing gratitude, and having the right mindset of not prejudging others. The overall message is that LinkedIn alone is just a tool and people must make the effort to use it effectively through relationship development.