WordPress.com automatically sends notifications to Google with every post and page update. The search engines can take 4-6 weeks or more to add any new sites. Read this page for more information about WordPress.com and Search Engines.
It will take a couple of days from the time you created your blog for to show up in WordPress.com search results.
You can control whether or not search engines index your site in your Privacy Settings in your dashboard at Settings > Privacy Settings.