By default the front page of your blog displays all posts. The 404 (page not found) error message on the front page of the blog appeared because the Admin of the blog deleted the placeholder Hello World post. http://en.support.wordpress.com/not-found/ As soon as you publish a post, not a page it will disappear. Read the differences between Pages and Posts.
The front page of the blog by default will display your posts (not pages) in reverse chronological order, with the most recently published post on top. If you do not want all the posts to show on the front page, then you can create a static front page called for example “Welcome” for your site and a “Blog” page for posts.
To do that create two pages http://en.support.wordpress.com/pages/ After you do that you go to > Settings > Reading and make the designation change and click “save changes”.
Front page displays
__ Your latest posts
A static page (select below)