Hello,

The instructions about parting will be included in the upcoming video tutorial for Cinema 4D. 

Meanwhile, I can show you some example of how it works. If something doesn't work as I show you then it's a bug. You can start by updating to the latest nightly build and trying again, if the problem persist please provide detailed instructions to reproduce the issue. 

Auto Parting: With this option the guide roots have to be far enough from each other to help  Hair From Guides determine if a parting should be applied. See the example gif and scene below: 

Use the distance threshold to refine the parting. 

Parting Channel: Paint a per-strand channel where one side of the parting is black and the other is white. It should look like this. To learn how to create and use strand channels check THIS link. 

Then apply the parting channel like this: 

I can confirm that the parting is not working with Vertex Maps, as well as the parting plane editing issue. We are investigating both issues and will be addressed as soon as possible. Thank you for reporting it. 

Edit: I included two test scenes to test Auto Parting and Parting Channels.