In fact the QDSCV does almost nothing -- it is WCF RIA Services that do everything.
The QDSCV has two important things -- the Load method and the AutoLoad property.
When you call the QDSCV.Load() method manually, the QDSCV will simply call the DomainContext.Load(query) method and send a request to the server. When data comes back it will fill itself with the entities that came from the server.
When the AutoLoad property is true, every change that somehow affects the EntityQuery will trigger a load from the server, i.e. just like calling the Load method manually. Those changes include filtering, sorting and paging.
The QDSCV can only contain one kind of entities, i.e. one entity set. If you want to load related entities, you can do this either with other QDSCV's or by using the Include attribute.
The main point here is that the QDSCV does absolutely nothing beyond building an EntityQuery<T> based on the current filtering, sorting and paging criteria and then simply calling the DomainContext.Load method. All of the job is actually done by WCF RIA Services.
All the best,
the Telerik team