I created a web site in https://sites.google.com/site/ but it can not be searched by Google even if I type a link directly.
If your content isn't already index this won't help. But please do consider following this guide that describes submitting your sitemap to the Google crawler, so it is indexed properly.
Googles crawling bot is crawling over the internet following links. If you have no links pointing to your site, it will be hard to find you at Google.
Since you are at Googles own domain, Google may find you, but you have to give it a few days, before Google finds you. Then, you can find your site when searching at your specific url.
If you want to rank higher at other keywords in Google, you have to look at something called SEO.