The second part is the domain name - or the address of the host of the web page. Search engines use automated programs called robots or spiders to travel constantly from site to site checking new web pages and updating pages and links. Some search engines index the full text of each page, others just index keywords. When you enter a search term or phrase into a search engine, the program checks your term against all the web pages it has indexed. Sometimes you'll get an amazing number of results, and you'll need to refine your search using the techniques you've learned in InfoTrekk.
Subject directories are web databases that use humans to index new web pages rather than robots.
In subject directories web pages are organised into categories and sub-categories according to content. Subject directories don't index nearly as many web pages as search engines, but they are good places to start if you are looking for information on a subject and you won't have to go through a lot of irrelevant hits. Yahoo and Magellan are good examples of subject directories. These are a little different in that they simultaneously search other search engines and subject directories. Searches need to be simple, but meta search tools can be a good way to start your search for information.