I strongly suggest using the step by step tutorial that Staff have linked to on the bottom of your Admin page http://learn.wordpress.com
re: this front page error
It seems we can’t find what you’re looking for. Perhaps searching can help.
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.
All support documentation is found at this link> http://en.support.wordpress.com
Visual editor > http://en.support.wordpress.com/visual-editor/