Some search engines use meta tags to get a better idea of what your page is about. There are only two useful metatags, "description" and "keywords" that you put in the <head> of your html document. The keywords help bring up your page for the words you input into the tag. The META description just complements the <title> tag. For example if you look for your url on google, it'll bring up a title and a description.
Don't make ridiculously long descriptions or keyword lists. They'll just slow down your page. Each keyword has less and less priority as you go down the list, so adding them to your content would count google more than keeping them on your keyword list.
While in the lesser search engines like scrub the web they are the basis of the rankings, search engines like google give them very weak consideration. They mostly help for very broad search terms. For example, if you type "shopping" as one of your keywords, it'll give you no hits, but typing "Dallas Texas Hats Shopping" it may just give you the edge for that keyword. Many sites have dominated the small keywords so specializing in specific terms is much more lucrative. To learn more on how to get top ranking read the how to get more hits article.