that simply says what charset is used for the page so the browser knows which 1 to use and also that is it html to the browser can pass it,
Some search engines etc still use meta tags and should be used still but alot of people do not bother. 1 mistake people make with meta tags is to constantly repeat words such as keywords this will actually get you blacklisted. Meta tags etc should be a maximum of 255 chars as well but the less keywords used for example in the keyword meta tag the more important they will seem to the search engines.