WordPress will automatically generate your meta tags based on your content and site description. If you want more control over your meta tags, you can hardcode them into the template you use by going to Appearance > Editor > Header (header.php).
Meta tags are now ignored by Google and some of the other Search Engines after some people abused the meta tag system for getting better placements in the Search Engines, but it is still worthwhile adding them as they can still support your content as long as they are relevant.
Since you are using WordPress you may want to use "All In One SEO Pack" plugin -
http://wordpress.org/extend/plugins/all-in-one-seo-pack/This will allow you to control your meta tags without having to edit your template.