A WordPress blog can either be structured as a page based website or its conventional post based blog structure can be retained. That’s why understanding the differences between posts and pages, comprehending the SEO implications of creating a page based structure, and knowing how to use custom menus are key to decision making when selecting a theme, and setting up your WordPress.com blog. http://onecoolsitebloggingtips.com/2010/05/12/better-blogging-at-wordpress-com-pages-and-posts/

See here for a step by step guide > Using WordPress.com to Create a Website http://en.support.wordpress.com/using-wordpress-to-create-a-website/
See also http://wpbtips.wordpress.com/2011/12/19/custom-menus/
This may also help http://onecoolsitebloggingtips.com/2011/03/06/multi-author-wordpress-com-blogs/