Usually plugin and themes needs to add menus in the Administrator panel for provide access to screens. The best way is adding a menu section in the Administration menu that allows the user to access the screens.
There are some functions for manipulate the Administration Menu.
osc_add_admin_menu_page(
__('Listing'), // menu title
osc_admin_base_url(true).'?page=items', // menu url
'items', // menu id
'moderator' // capability
) ;
osc_add_admin_submenu_page(
'items', // menu id
__('Manage listings'), // submenu title
osc_admin_base_url(true).'?page=items', // submenu url
'items_manage', // submenu id
'moderator' // capability
) ;
...