Mesh Directory Service is a central web user interface very similar to WAYF (Where Are You From) pages in identity federations. It takes metadata from the Central Database and provides a user interface for users to choose their home/preferred sync’n’share systems to establish trust to.
The service is mainly used in the invitation scenario. The basic principle is as follows: suppose you are using your Mesh-enabled EFSS source system. You want to share data with your colleague and you have no idea what system the target user uses. You send an invitation that directs your colleague to the Mesh Directory Service to choose the target system.
If you followed the path recommended by these notes, congratulations, you now have basic understanding how the mesh federation works. And you should be ready to configure your site to join.