Meta Tags contain information about your page rather than information that will be displayed on your page. The major purpose of meta tags is to instruct search engines (for example Yahoo, Altavista, Lycos, etc.) how your page should be indexed. A web site that has not been indexed by any search engines is a lot like having an unlisted phone number. Somebody could accidentally call you by dialing random number combinations, but without a listing somewhere, you will not be accessible to people who want to find you.
The search engines are like huge directories of information. Unfortunately, they are so huge that it is easy to get lost in the shuffle. To some extent, you can control how your site is indexed by the major search engines to maximize your site's chances of being seen by the right searchers. The major meta tags are "description" and "keywords".
The syntax is as follows:
<META NAME="description" CONTENT="ShtetLinks site for the former Jewish Shtetl of Lazdijai, Lithuania">
<META NAME="keywords" CONTENT="lazdijai, lazdei, lozdzieje, lithuania, genealogy, jewish, shtetl">
These lines should go between the <HEAD> tag and the <TITLE> tag at the top of your page. The examples above are for the main page of the Lazdijai site. Notice that in the "keywords" section, there are several alternate spellings. That is to help in case anyone searches using those spellings. It is also a good idea to put common misspellings in the "keywords" section. Put as many keywords as you wish, separated by commas. The "description" should be a relatively short phrase which describes the site or page.
You can put these meta tags on each page of your site, if you wish. When you submit your site to the search engines, some will index each page of your site, some will just index the home page. The more pages you have indexed and the more keywords that are indexed, the greater the chances that somebody will be able to find your information.
The Art of Business Website Promotion has a very good explanation of how search engines work and more information about meta tags.