explanation of server roles

Is there a decent document, besides that abstract garbage found in TechNet
that describes each server role for FCS?

I'm looking for something that will actually tell me what these roles do and
not just name them.

Reporting Database Role
Management Collection Reporting Role
Distribution Server (I know what this one is and does)

I need descriptions and I haven't found them yet. Honestly it shouldn't be
this difficult to find this but it has been.