"A surprisingly simple, flexible layout solution made possible by placing fields in regions. Region View Modes is just a bit of glue to join Drupal's theme regions and View Modes."
This blog post, written by the maintainer, explains the module very well, use this as a starting point to understanding it: http://singlebrook.com/blog/super-simple-drupal-layout-with-region-view-modes
Demo vid from same blogpost: http://youtu.be/ttIQ1L0ovOA
Demo notes
The Region View Modes module allows you to place fields of a node into theme regions. The location of the fields is set per content type and does not appear to be overridable per node. You can choose whether the fields appear above or below the normal blocks. This is all controlled using view modes.
Use the Block Reference module to insert blocks into nodes. This module adds a field type which allows you to reference blocks.
The Multiple Select module lets you order your selections in a multivalue select list. The field edit widget provided by core is a regular dropdown where there is no way to order.