To get a reference to a specific admin page (such as Dashboard), we can use the admin_url(), network_admin_url() or get_admin_url() functions, like so:
get_admin_url( 'index.php' );
You will need to pass the reference to the page you’d like to display. To find out how, simply click on the menu page in question, then look at the URL. Anything after wp-admin/ is the parameter.
Those functions are described in detail in the WordPress Codex: