problem DLL logic

[C# Programming]

i hav a project with a DLL (someone created this),
suppose in this project a form (frmmain) contain some textboxes, combobox and some button also as save,Edit, delete..

suppose record loaded by RecordID-
so he just call
objDLL.LoadRecord(this)
and record filled in text boxex and combobox, radio button

and clicking on save- programmer just call
objDLL.hndRecordSave(this); //// as form name is same frmMain
and record saved, record of textboxes, combo, radio, etc

similarly on edit he just call
objDLL.hndRecordUpdate(this);
and record updated.

i just wana to know at ceating dll how he manage all form in function and how he create this dll. and now i wana to implement it to add and remove some field according to requirement.

thanks hoping u all understand what i want to say.