WordPress allows you to create your own menus in the admin area, to do this you can use the function add_menu_page().
Sometimes I've needed to build a new page outside of WordPress but still have the ability to access the WordPress database from this new page. This would normally use custom tables you've created. To access the WordPress database normally you would just need to use the global variable $wpdb. This object connects to your database using the credentials found in the wp-config.php in the constant variables DB_NAME, DB_HOST, DB_USER, DB_PASSWORD.
In WordPress there is a special HTML comment called more. \
When you setup a new site with WordPress multisite you have the option to create your site as sub domains or into sub folders.
When you upload an image to Wordpress by default it will be converted to three different sizes.