The meta description tag describes your site's content, giving the reader and the search engine an accurate summary filled with multiple keywords.
Meta tags are hidden in the document's source, invisible to the readers. Some search engines, however, are able to use meta tags as a part of their algorithm. Engines do not penalize those who use meta tags properly, so it's recommended that you always include them.
A meta description tag can boost your rankings on some engines.
Use it on all pages
Limit it to 150 characters
Should contain keywords
Keywords shouldn't repeat more than 7 times