The icons you see here are quick links to some of the most popular social bookmarking and social networking websites.
Clicking on any of the icons will let you store and share a link to the page you are currently viewing. You will also be able to access the link from any computer you are using.
Each Social Bookmarking / Social Networking site works differerntly, so if you're not already a member of one of these sites, pay a visit to them to see which one suits your needs best.
You might also find this article on WikiPedia useful.