Hello, Roban , what is site description or key words either ? What is the function of it ? And how should I put it ?! Sorrry.
My favorite topic, so I HAVE to reply :-)

The information provided at meta tags "keywords" and "description" are used by search engines to categorize and rate your website.

These two tags are mainly responsible for getting a good (or insufficient) ranking position. Well, this is too simplified, of course - there are many other factors deciding about how a search engine will rate your site. But while the meta tags are not a magical solution, they are definitively important.

Therefore it is essential to have at least these two meta tags on every (!) page of your website. In fact, there are also other meta tags like "author", "copyright" and also some quite specific ones for special purposes.

You can learn more about meta tags at http://www.w3.org/TR/html401/struct/global.html#h-7.4.4

Basically I recommend the following for keywords/description:

"keywords": A comma separated list of words and phrases that match your business, respectively the concerned webpage (sorted by importance, so the best matching ones have to appear first).

Use about ten to twenty entries; not more, unless it makes sense and please avoid unrelated keywords, your competitors' company names and trademarks (legal reasons) as well as such over-used words like "free" or "sex" - even you offer this ;-)

"description": Around two to three full sentences about your business, products and service, main market and other related information. Consider that the description appears usually in search results, so use good-styled English (spelling), avoid repeating, capital words and your domain name (since it is not required to have it there).