Facebook is a social utility that connects people with friends and others who work, study and live around them. People use Facebook to keep up with friends, upload an unlimited number of photos, post links and videos, and learn more about the people they meet.
LinkedIn strengthens and extends your existing network of trusted contacts. LinkedIn is a networking tool that helps you discover inside connections to recommended job candidates, industry experts and business partners.
Twitter is without a doubt the best way to share and discover what is happening right now.