The information that you provide in a meta tag is used by search engines to index a page so that someone searching for the kind of information the page contains will be able to find it. The meta tag is placed near the top of the HTML in a Web page as part of the heading.
This is information that is not visible to users on a website, but is loaded into areas of a web page to be found by Search Engines and help them rank the site in results.
If you are referring to meta name="keywords" and "description", the search engines do not pay much attention to them anymore. They concentrate on the code that makes up the ON PAGE content (as well as may other elements).
Mind you, if you can come up with a short meta "description" that can catch the eye of the user as they scan though a search engine result page - well then that would be a massive plus for traffic to your site.
Meta Tags do not affect the appearance of a web site and are not visible when you look at a Web page, but they provide information regarding the content of the site. Meta Tags are used primarily by search engines that scan through the programming code and text of each page.
When you submit a web site to a search engine, that search engine sends out a robot called a "spider" or "crawler". This robot is a program that looks at your site, decides if it will be indexed, and then (if you're accepted) looks through your web page more thoroughly before finally indexing it into a specific search engine database.