Oracle: select insert

Does anyone knows what this "select 'insert..." clause means? It looks like that it generates a lot of insert statement. Are there some introduction material telling about that?

==================create_portlets.sql============================
set pagesize 999;
set linesize 320;
set feedback off;
set verify off;
set heading off;
SET TERM ON;
SET ECHO ON;

SPOOL tmp_create_test_data.sql;

-- Login (user, pwd)
select 'INSERT INTO NPP_PLACEHOLDER_PORTLET_MATCH (PORTLET_DEFINITION_ID, PLACEHOLDER_DEFINITION_ID, ACTUAL_SIZE) VALUES ('
 || pf_portlet_definition.portlet_definition_id || ', '
 || pf_placeholder_definition.placeholder_definition_id || ', '
 || '1' || ');' from pf_placeholder_definition, pf_markup_definition, pf_portlet_definition  
 where pf_placeholder_definition.markup_definition_id = pf_markup_definition.markup_definition_id
 and pf_portlet_definition.portlet_label = 'portlet_userpwdlogin' and pf_portlet_definition.webapp_name = 'portal'
 and pf_markup_definition.markup_type = 'Placeholder';

-- Registration
select 'INSERT INTO NPP_PLACEHOLDER_PORTLET_MATCH (PORTLET_DEFINITION_ID, PLACEHOLDER_DEFINITION_ID, ACTUAL_SIZE) VALUES ('
 || pf_portlet_definition.portlet_definition_id || ', '
 || pf_placeholder_definition.placeholder_definition_id || ', '
 || '1' || ');' from pf_placeholder_definition, pf_markup_definition, pf_portlet_definition  
 where pf_placeholder_definition.markup_definition_id = pf_markup_definition.markup_definition_id
 and pf_portlet_definition.portlet_label = 'portlet_registration' and pf_portlet_definition.webapp_name = 'portal'
 and pf_markup_definition.markup_type = 'Placeholder';

SPOOL OFF;

set pagesize 55;
set feedback on;
set heading on;

@tmp_create_test_data;

commit;

=============================

====================
SQL> -- Login (user, pwd)
SQL> select 'INSERT INTO NPP_PLACEHOLDER_PORTLET_MATCH (PORTLET_DEFINITION_ID, PLACEHOLDER_DEFINITION_ID, ACTUAL_SIZE) VALUES ('
  2   || pf_portlet_definition.portlet_definition_id || ', '
  3   || pf_placeholder_definition.placeholder_definition_id || ', '
  4   || '1' || ');' from pf_placeholder_definition, pf_markup_definition, pf_portlet_definition
  5   where pf_placeholder_definition.markup_definition_id = pf_markup_definition.markup_definition_id
  6   and pf_portlet_definition.portlet_label = 'portlet_userpwdlogin' and pf_portlet_definition.webapp_name = 'portal'
  7   and pf_markup_definition.markup_type = 'Placeholder';

INSERT INTO NPP_PLACEHOLDER_PORTLET_MATCH (PORTLET_DEFINITION_ID, PLACEHOLDER_DEFINITION_ID, ACTUAL_SIZE) VALUES (77009, 2001, 1);                                                                                                                                                                                              
INSERT INTO NPP_PLACEHOLDER_PORTLET_MATCH (PORTLET_DEFINITION_ID, PLACEHOLDER_DEFINITION_ID, ACTUAL_SIZE) VALUES (77009, 2002, 1);                                                                                                                                                                                              
INSERT INTO NPP_PLACEHOLDER_PORTLET_MATCH (PORTLET_DEFINITION_ID, PLACEHOLDER_DEFINITION_ID, ACTUAL_SIZE) VALUES (77009, 2003, 1);                                                                                                                                                                                              
...