If you flag a property as being the source of the detail data (PropertyRelation attribute) and set AutoCreateDetailConfigurations to true, you should automatically have details appear. If you see the details, then you either have a Pro license key or a non-expired trial key.

If you want to provide default detail configurations, then you can play with the grid's DefaultDetailConfiguration property.

If you want to provide explicit configurations for specific detail configurations, then you can use the grid's (and DetailConfiguration's) DetailConfigurations property.

If I add DataGridCollectionViewSource.DetailDescriptions and DataRelationDetailDescription with DataRelationDetailDescription.ItemProperties for the detail row I get no expand/collapse option and no detail rows at all. 

If you want to define the item properties that will appear in the details, then you will need to define PropertyDetailDescriptions rather than DataRelationDetailDescriptions, and specifying the property name in the data source that contains your data. Now this may seem conflicting with the previous advice; however, keep  in mind that flagging a property as containing the detail data (PropertyRelation attribute) will result in the automatic creation of  PropertyDetailDescriptions (in the case where they are not explicitly defined in the DataGridCollectionViewSource/DetailDescription's DetailDescriptions property).

I suggest you take a look at the following Master/Detail topics for more information and examples:

DataGridCollectionView Overview
Master/Detail Overview

Hope this helps!