Meta tags are used by some search engines to help determine what your site is about so it can be matched to relevant search queries. It's only one of many 'scores' they use in ranking sites, but any edge is an advantage, however small it may be. Meta tags also provide the description some search engines use in describing your site in search results.
The free meta tag generator below will help you get them formatted right. Who loves ya, baby! The tags generated should be placed into the <HEAD> section of your page, just below the title.
NOTE: For a more comprehensive set of meta tags and handy offline convenience, check out my MetaTag Master software. You may also be interested in CSS Master for easy Cascading Style Sheet creation.