API to display block in regions
Instead of using the admin blocks interface, if you really want to manually render blocks, you can render:

Directly in a template: 

if ($block = module_invoke('module_name', 'block_view', 'block_delta')) {
  print render($block['content']); 
}


Via code, with drupal_add_region_content

if ($block = module_invoke('module_name', 'block_view', 'block_delta')) {
  drupal_add_region_content('left',  $block['content']);
}