Generic Collections and Generic Dictionarys

Idea: To use generic collections and dictionarys.
Background: Collections-Overview

1. Get an overview of the different Interfaces and Classes in the Generic Collections and Generic Dictionary.
   
2. What is Class HashSet and what is the connection to the GetHashCode( ) method in class Object?
   
3. What is IEnumerable<T> and what is the purpose of the Interface?
   
4. How to sort and search in a Collection?
   
5. Create a class Items, and a generic catalog to contain Items. Make Comparer Classes to compare Items after different criteria. Make a GUI to display a list of Items, it should be possible to display Items sorted by different criterias - look at: SortItems