This tool will analyze a website's META tags. Although the use of META data is certainly in question, analyzing a competitors 'keyword' and 'description' META values is a good way to find ideas for keyterms, and effective copy for your website.
Keywords: This should contain a short list of keywords and terms related to your site. Generally they should be separated by a comma, but some people prefer not to use any sort of delimiter.
Description: This should be a brief description about your site, and what it offers. This is sometimes used by search engines as a websites 'snippet' for search results .
About Meta tags At one point Meta tags where a considered a relatively important factor by search engines. AltaVista and other older search engines used them to help determine a sites theme, and relevance to a given term. This is no longer the case, search engines now rely on much more advanced techniques to do this. That said, META tags still have a some life left in them; they are sometimes used as the snippet of a site's content in search engines result pages by Google, and possibly other search engines. It's also possible they still have a slight influence with some search engines in determining a sites content.