Drupal 8 significantly simplified content migration from older Drupal versions. There is currently an issues if you migrate content that contains dot. How to fix it is described in this article.
Stable version of Drupal 8 has been here for a while. As successor of Drupal 7 brings huge changes and new features (in good way) that are available in basic installation of Drupal 8. One of those features is migration. Big task in Drupal 8 was to allow relatively easily migrate older versions (Drupal 6 and Drupal 7) to Drupal 8. Migrate API defines set of processes to allow transform and customize all data structures from older Drupals to Drupal 8. Drupal is capable to create a lot of transformations by itself (with some extra modules) but sometimes it is needed to customize certain parts of migrations.