All About Meta Tags And Meta Tag Descriptions
The meta tags of a web page are for the most part, unseen by your viewers, yet very important to search engines in helping to understand your page. The most important tag is the title tag. This is what will usually show up in the search results. It can make or break whether or not the viewer clicks on to your site.
Another tag often overlooked is the image alt tag. If you have images on your site, this tag should be used every time without exception. Use of this tag every time can add up to a significant boost in traffic.The full explanation can be found at http://wpbtips.wordpress.com/2011/04/04/adding-meta-tags/
The meta description is sometimes used by search engines, though not so much these days. Still, it is important to write a little 2 sentence description and use the tag on all your pages. Manyof the smaller search engines still use this tag for ranking, and even some of the big ones will display your description on the search results under your meta title.
The keywords meta tag is for the most part, not used anymore. Still, you should fill it out. Do not over do it or over-think it. Just put in a few relevant key words.