When you are in Internet Explorer, for example, there is an option to bookmark a site or "add to favourites". If you bookmark lots of sites then you can subdivide your list of favourites into folders.
This is fine until you find yourself at another PC - because you are in the library, or at home, or in an Internet cafe. At that point your bookmark is stuck there on another PC and you have to Google for the website you want.
One solution is social bookmarks. This is a way of using (usually) free software to make bookmarks that are then stored on the Internet, rather than on a specific PC. That means you can access them wherever you happen to be. It also means you can share them with your friends or colleagues.
Online bookmarks can also be subdivided, although you use "tags" - descriptive labels - rather than folders. You can look at other websites that other users have tagged with tags you use to see if you can discover more sites of interest. You can also put a gadget on your toolbar that you can bookmark sites you visit in one click.
The library website uses one of these social bookmarking systems - del.icio.us - to make up a set of quick links. I just set up a link once to each page of tags and I can change the bookmarks on the pages as often as I like without having to update the library website each time. You'll find more social bookmarking facilities listed on Phil Bradley's very handy website.
Gadget users are a fickle lot, and I've got bored with del.icio.us. I forget to go and look for the things I've put on there, I forget to update. I'm now adding bookmarks to my iGoogle page. That means they are to hand whenever I'm on the Internet and I don't have to remember an extra password. I can organise them using labels and I can add a site fairly quickly to my bookmarks. As I'm starting from scratch again I don't have many bookmarks. I have yet to find a gadget that stops me bookmarking so many things that it starts being quicker to Google for a site than trawl through all my bookmarks....