If you want your main page, www. yourdomain .com to only show posts for that main root, without showing post from all other categories, go to categories and change your category ID #1 (normally called uncategorized) to "Main Page" with the slug of "www" no quotes. Or create a new category that has the slug of www . As long as your site uses the www, it works.
Pretty cool hack. Surprised it actually worked. LOL