Question on migration from Joomla to Drupal

Hello, dear experts!
I am writing here not from a good life, I feel the following need:
There is a task to transfer data from Joomla to Drupal 6, rummaged through the whole forum, but found nothing convenient.
There is such a material: www.drupal.ru/node/22339 , but the level of presentation is not sufficient for my understanding.

If you are faced with such a situation and are able to set out in a popular and detailed way, then please set out on the right path.