Google Reader is an application within your Google account that allows you to subscribe or follow blogs and websites. Simply put, that means you can choose your favorite blogs and websites and have their content sent to you as soon as it is updated, rather than having to keep visiting the site to see what is new. Think of it like your own personalized newspaper or magazine. New content delivered to you, instantly.
Subscribe to blogs and websites that you want to share with your students, or if they are old enough, help them set up their own Reader account so they can start exploring topics of interest on their own.