Neither of you are making sense. "How to get a specific for a site?" A specific what?? Keyword??? When you make a website, it's based upon a particular subject. Take a pen and paper, write down the words related to it. Ta-da. You have your keywords. If you mean something else, rephrase your question.
If you want to choose the keywords for your website then you have to look up to your website, see it's basic service i.e for what purpose it has been developed, after that according to your website services, you have to choose specific keyword which will be relevant to your website services or content so as to drive traffic to our website relevant to these keywords.
Use Google ad words Keyword Research tool and also use Word Tracker for searching best keywords for your website.
Try google adwords keyword tool. Just enter the website URL and it will suggest you the keywords where you can choose or you may get keyword ideas similar to the resulted keywords.
use Google Adwords Keywords Tool do define which keywords do suite your product. Most important is high conversion rate and niche enough . Make sure that it not too high competition, high local search and global search.
you'll want to use google's adword tools to find a select keyword to focus on, otherwise you'll be building your website blindly and simply hoping that you'll receive traffic for whatever you write, which would be more of a social networking thing rather than a search engine optimization thing. if you do this, then you can also use google's adword tool to generate keywords based on your webpage(s) (frequency of keywords and density). and when choosing a keyword, you'll want something that isn't too competitive. i don't really pay attention to the competition column on google's adword tool, but search for it myself. if the competitive sites in the serps are sites like about.com, wikipedia.com, etc, i don't go for it. because those sites are already well established. best of luck!
According to me you can use Google AdWords Keyword Tool. This tool can help inform us how a lot a keyword is individual optimized for by competitors.