Inclusion in Google's search results is free and easy; you don't even need to submit your site to Google. It happened so that Google is a fully automated search engine that uses software known as "spiders" to crawl the web on a regular basis and find sites to add to their index.
when I just search on google using the title of articles, I can't find out them.
If use site: domain then shws means its indexed.. but if use the title of the article for searching means its related to the SERP ranking.. the site is new so its natural.. will take some time and also need some good effort on promotion to get a good position in SERP
Check for crawl errors. The Crawl errors page in Webmaster Tools provides details about the URLs in your site that we tried to crawl and couldn't access. Review these errors, and fix any you can. The next time Googlebot crawls your site, it will note the changes and use them to update the Google index.
Also make sure that the URLs haven't been blocked with meta tags.