So basically you are mentioning of type List etc.
If you want to add values to the list accepting input from user from form fields and then add to the existing list in model. the easiest but not so elegant way would be
suppose you have class "Person" and then List in your model. first create an instance of person that will have empty person instance , add it to list and then bind this last list item to your edit for.
@{
Person contact = new Person(); //Empty person instance
PersonList.Add(contact);
}
later on bind this to your induvidual fields
@Html.TextBoxFor(m => m.PersonList[PersonList.Count - 1].PrimaryContacts.FirstName)
This works good for Validation on model properties as-well and also after every form submit, for next inclusion you just add the new person. but take care to write the remove peice of code if form is cancelled.