How do I print a menu with links generated by my custom module?
Menus and paths are slightly different things...in hook_menu() you're defining paths that can be consumed; menus create the links to those paths - the two concepts aren't necessarily related (a path can exist without a menu link).

You can assign a particular router path to a menu using the menu_name property in your hook_menu() items, but that menu needs to exist already. 

Fortunately Drupal provides a method for adding links to the top of a page through hook_menu(), and you only need to change one line:

$items['admin/custom/add'] = array(
  'title' =&gt; t('Add Custom'),
  'decription' =&gt; t('Add custom'),
  'page callback' =&gt; 'custom_add',
  'access arguments' =&gt; array('add custom'),
  'type' =&gt; MENU_LOCAL_ACTION, // &lt;-- This one changed
  'file' =&gt; 'custom_add.inc',
  'file path' =&gt; drupal_get_path('module', 'custom') . '/includes',
);


That will put a link to 'Add Custom' at the top of the 'admin/custom' page; if you're using the Seven theme for administration it'll look like the 'Add Content' link on the content admin page: