Save multiple nodes to a person

hello,
its my first message here so here we go, hope you can help..

Technology: Windows Forms
Framework: .NET Framework 4.0
Programming Lang: C#
Current Knowledge: Begginer(+)

Question?
I am building a management system for learning/teaching purposes.
Form Controls:
- TreeView that contain categories of report.
- ComboBox With Worker that added the report.
- ComboBox With Student name reported on.

1. In the form I have a treeview that filled with nodes (as categories and sub-categories) from database table.
this table contains 3 columns: "ID","Description","ParentID".
2. I would like to allow the user(Worker) to "save" (=relate) multiple nodes/categories to a specific student (student name will be chosen from a combobox), on a specific datetime (means one row on relation table / junction table).

my question is divided into three:
First, the database part (continue current design, mabye add a relational table that will hold foreign keys from nodes and students table).
Second, the c# code, how to implement this.
Third, Consider I will need to retrieve this data (for each student that has specific categories for a specific datetime) - i think each report = one row in table.

Thanks..