Newbie: Pecursor to Delegates

[CuriousOne]

Hello, all. I'm trying to teach myself C# basics largely because I found its syntax cleaner in addition to it being used for an upcoming grad course.

I am trying to follow code in this book, which has been fine up until the preliminary to delgates. Specifically:

An abstract class is given for DocumentProcesses:

abstract class DocumentProcess
   {
     public abstract void Process(Document doc);
   }

The processes take the form of:

class SpellcheckProcess : DocumentProcess
 {
      public override void Process(Document doc)
   {
       DocumentProcesses.Spellcheck(doc);
   }
 }

Document is a defined class with simple properties. Question 1: Why didn't they just use an interface if there's no "default" code needed and a must-have override?

The Document Processor has the code as follows:

class DocumentProcessor
           {
              private readonly List<DocumentProcess> processes =
              new List<DocumentProcess>();
              public List<DocumentProcess> Processes
              {
                  get
                  {
                     return processes;
                  }
              }

             public void Process(Document doc)
             {
                foreach(DocumentProcess process in Processes)
                {
                   process.Process(doc);
                }
            }
      }

Question 2: Since the list is a readonly field and private, how can it be accessed via anything other than a constructor?

This block of code seems to do just that (the author does not mention it as a part of the DocumentProcessor class):

static DocumentProcessor = Configure()
 {
   DocumentProcessor rc = new DocumentProcessor
   rc.Processes.Add(new TranslateIntoFrench); //etc...;
  }

This seems to be accessing the Processes Property, which only has a get. Question 3: How is this accessing the private readonly List, especially to add processes?

And later:

DocumentProcessor processor = Configure();

-- in a Main method
Question 4: I understand that Configure() returns a DocumentProcessor object to this reference, but how does it do so? This confusion is related to questions 1-3

Thanks. I'd really like to move on to delegates, but I want to understand this first as opposed to memorizing it. I apologize for the indentation.
_CuriousOne