As you are probably aware, the Internet is huge, so huge in fact that no single entity could ever hope to categorise it all.  There are Web Sites that specialise in this categorisation of the Internet and there are also Web Sites that specialise in the indexing of the Internet.  These Web Sites are known as Search Engines. 

The search engines that specialise in categories are (funnily enough) category based.  So every link to a web site on the search engine is put into a category.  Educate the Children, for example, might be listed on a search engine under the Education: Elementary category.   A good example of this would be Yahoo! or the UKDirectory.

The search engines that specialise in indexing, basically enable the internet user to search through the contents of millions of Web Pages.  Key words are used when searching, e.g. a search for the key words "Educate the Children" would come back with a listing of all web pages containing all those words, hopefully this site!   A good example of this would be Infoseek or HotBot.

Both types of search engine allow the searching by key words, but remember the main difference is the information stored about the searchable web pages: Category based - Category, key words, brief description.  Indexed - Key words, brief description, the actual content of the page.

TIPS

When using category based search engines, click on the category, sub category you require, then do a keyword search within that group of categories.  This will give you results that are most relevant to what you are looking for.

When using keywords, try to be specific, i.e. you want to find a lesson plan on space type in:  space lesson plan solar system.  Don't be afraid to use the refine search option, this simply performs a search on the current results of your last search.  So for the above space lesson plan example you can narrow the search down to just a primary lesson by adding the word primary and clicking on refine search.

Try using the search engines for specific web sites, these will only find information on the web site you are on, and is a quick way to find out whether a big site has the information you require without having to navigate it all!

Use different search engines if you can't find what you want, try: Yahoo!, HotBot, Lycos, Excite, AltaVista, Infoseek, WebCrawler and lots more...

If you are looking for information that is country specific, try a country specific search engine like Yahoo UK, Lycos UK, Excite UK, UKDirectory etc...