hi, when you do a search for a keyword phrase with quotes it means google will show results for that exact phrase, without quotes it gets a little more difficult to rank for that exact phrase but the reasons for that are to numerous to mention.
If you are doing Seo of your site go with keywords/key phrases without quotes. The reason behind is as follows: a normal surfer will not have any idea about whether to use quotes or not. The surfer will just surf the net without puting any quotes. Also, if you are using your keywords/keyphrases for Google adwords then you can go ahead and use Quotes, that is fruitful. Cheerz