As aforementioned, Drupal migrations give you many tools to migrate content, but these are some of the basics to get you started with D6 to D7 migrations for OSU’s site content. More information on all these topics can be found in Drupal’s API and in various issues on drupal.org. I found some of these pages to be useful when learning about migrations:

 A good introduction to migrate_d2d:

 http://www.acquia.com/blog/drupal-drupal-data-migration-part-1-basics 

http://www.acquia.com/blog/drupal-drupal-data-migration-part-2-architecture

More information on prepareRow():

https://drupal.org/node/1132582

Field mapping:

https://drupal.org/node/1133448

http://drupalcontrib.org/api/drupal/contributions!migrate!includes!migration.inc/function/Migration%3A%3AaddFieldMapping/7

Registering migrations:

https://drupal.org/node/1824884

Migrations with Organic Groups:

https://drupal.org/node/2023273

Drush Migration Commands:

https://drupal.org/node/1561820