https://docs.kolab.org/architecture-and-design/ldap.html#a-kolab-resource, but I think it's wrong/incomplete.
You'll also have to configure how to get them. Here's an example from a Kolab installation.
// LDAP directory configuration to find avilable resources for events
$config['calendar_resources_directory'] = array(
'name' => 'Kolab Resources',
'hosts' => 'localhost',
'port' => 389,
'use_tls' => false,
'base_dn' => 'ou=Resources,dc=mgmt,dc=com',
'user_specific' => true,
'bind_dn' => '%dn',
'bind_pass' => '',
'search_base_dn' => 'ou=People,dc=mgmt,dc=com',
'search_bind_dn' => 'uid=kolab-service,ou=Special Users,dc=mgmt,dc=com',
'search_bind_pw' => 'password',
'search_filter' => '(&(objectClass=inetorgperson)(mail=%fu))',
'ldap_version' => 3,
'filter' => '(|(|(objectclass=groupofuniquenames)(objectclass=groupofurls))(objectclass=kolabsharedfolder))',
'search_fields' => array('cn'),
'sort' => array('cn'),
'scope' => 'sub',
'fuzzy_search' => true,
'fieldmap' => array(
// Internal => LDAP
'name' => 'cn',
'email' => 'mail',
'owner' => 'owner',
'description' => 'description',
'attributes' => 'kolabdescattribute',
'members' => 'uniquemember',
// these mappings are required for owner display
'phone' => 'telephoneNumber',
'mobile' => 'mobile',
),
'class_type_map' => array(
'kolabsharedfolder' => 'resource',
'groupofuniquenames' => 'collection',
),
);