Beneath whatever text you've read or video you've watched, there reside two, three or sometimes many more little graphic elements, huddled together as if to mock you with how little you know and how much there is to learn about this medium.

The Web site of The New York Observer, observer.com, is typical. At the bottom of a piece, a box says "Article tools." The first two are old school: "Print" and "E mail," with corresponding little images of a printer and an envelope. Easy enough.

But then come 11 other icons, all in a row, with no text to explain them. Among them are the recognizable Yahoo, Google and Facebook symbols, but things get more esoteric from there. There's an "SU," a little Martian-looking figure, and a twig or branch of some sort.

Mouse over the icons, and you do see text. You learn you can use one to "Digg this post on digg.com," another to "Bookmark this post on del.icio.us," a third to "Submit this post on Stumble Upon."

What you are seeing are sometimes known as "chicklets," or "social bookmarking chicklets," sort of like the rectangular gum of yore, sort of like the term "applet," which is a mini-software application. They are some of the building blocks of Web 2.0.

Web 2.0, a term that's been kicking around long enough to be old school itself, is dedicated to the proposition that nothing exists on its own; it's all part of a maelstrom of material constantly being identified, labeled and shared by users, becoming richer and more useful thanks to the effort.

With its emphasis on the collective, Web 2.0 also suggests that the 87-item Web-site bookmark list you keep, all to yourself and only very roughly organized, is so 2002.

So, back to the Observer example, if you click the icon with the Facebook symbol, up pops a window that will let you post the article to the Facebook page that you, of course, have by now.

Anyone in your "friends" network, which you also have, can then see and comment on the article, and it quickly becomes like the Algonquin Round Table, only without all the drinking.

The Digg icon lets you submit the article to the news site digg.com, which builds its content out of what its users submit and vote on as being worthwhile.

Stumble Upon (stumbleupon.com) also builds a catalog of material from user recommendations but adds the element of serendipity. Click "Stumble" and be taken to a new site; the idea is discovery.

The possibilities are nearly limitless. Add This, a site that collects popular icons and allows those who run blogs or other sites to easily add their own quick-link buttons, lists 36 services and their corresponding icons.

The executives of one of the services, faves.com (formerly Blue Dot), said they have counted at least 50 competitors occupying one corner or another of what is known as the social bookmarking space. Profy.com, a site that tracks Web 2.0 news, says there are nearly 100.