I installed the Migrate module, but I can't use it, nor can I find any useful documentation that explains how to use it. The page on /admin/content/migrate is empty.
How can I use this module?
The Migrate module only provides a flexible framework for data migration into Drupal. The logic and data mappings to perform an actual migration are pretty complex. Migrate does not provides an UI to build or configure your migration. IMHO, this is good because a complete UI to build such script would be at least as complex as writing it directly in PHP.
Its documentation is pretty complete and provides all the information needed to start using it. I recently started to use it and, coming from an OOP background, find it intuitive and easy to learn.
Speaking as one of the maintainers, Migrate is kind of a pain at first with but once you get up to speed on it's really powerful. The biggest change between version 1.x and 2.x is as MPD noted the lack of of the Table Wizard. It's now all class based which makes it trickier to setup a migration but much more flexible. Instead of having to get all your data into MySQL now you can use a variety of different sources.
I've got some slides that might be helpful: http://denver2012.drupal.org/sites/default/files/Migrate.pdf
Cyrve developed the module and they have a post on the blog entitled Performing a data migration with migrate module that might be helpful.
Also, the video from the Migration: not just for the birds presentation at Drupalcon DC 2009 is probably somewhat out-of-date, but it should provide a good overview.
Migrate 2 is powerful. Just spent some time to learn it you won't regret.
Here's a full example of migrating contents to Drupal 7.
http://miss-hana.com/migrate-contents-from-drupal-6-to-drupal-7-using-migrate-2/
Very nice documentation in the answers.
Personally I found this post very helpfull
Are you accessing it as the admin user (uid 1)? If not, I suspect you need to explicitly assign permissions. Goto /admin/user/permissions, find the "migrate module" heading, and assign permissions as needed.
The last time we used this module, we did it in conjunction with Table Wizard.
To be honest, I just find it easier to write manual import scripts, rather than work within the confines of these modules.
This link might might help explain more about migration. It contains screen shots as well as examples. it gives a step by step approach to migration. http://www.lullabot.com/articles/drupal-data-imports-migrate-and-table-wizard. This link give a brief explanation on how to migrate content http://btmash.com/article/2011-02-25/migrating-content-using-migrate-module. I found think link about migrating the cck construction it. It might be worth a look as well. http://drupal.org/node/1144136
It's possible to move your website content directly from your Drupal to Joomla without using the importer module. You may try cms2cms tool that migrates site content via the connection bridge that is created between your sites. Such process requires both of your sites Drupal and Joomla being available online. Here you may watch how this converter works http://www.youtube.com/watch?v=cCkW-vwzlEg
But, if you want to move custom type posts, I'm not sure this tool will work as well with the migration of your theme.