What directories are
Directories are organized categories and sub-categories of links to websites. Almost every search engine nowadays has a directory of some sort in addition to its search service. The way most of these directories are created is that when the search engine spiders scour the internet and bring back information about a new webpage or website, the search engine use its own logic to put the webpage or website in one of the many categories it has in its directories.

There are, however, two web directories that use humans to read, evaluate and then categorize new webpages - Yahoo and Open Directory. Because humans do the categorization, it is often much better than machine controlled categorization. In addition, the humans evaluating webpages for these two directories are selective in what sites they will put in their directories and only the better websites make it. These factors make these two directories the best to use.

How to use directories
When you have only a vague idea of a topic area, you can browse down through subject matter categories and sub-categories of directories.

Example: A high school student who has to do a term paper for her biology class and thinks she might be interested in doing something on genetic engineering but has no specific topic in mind and wants to see what is out there. In this instance the student might go to Yahoo and click on its the Science category in its directory listing. Within Science she would click on Biology...then Genetics and then Genetic Engineering and so on. Somewhere along the way she might find a website that interested her or find more specific keywords with which to use in a search engine.