// Create post object
$my_post = array(
  'post_title'    => 'My post',
  'post_content'  => 'This is my post.',
  'post_status'   => 'publish',
  'post_author'   => 1,
  'post_category' => array(8,39)
);

// Insert the post into the database
wp_insert_post( $my_post );