What is the purpose of static class, interface and abstract class?

They have nothing to do with real time. Let me explain what they are:

A static class is a class where all methods and members are static, in other words there is no class instance. This means that you don't have to instantiate it, you can just use it as it is. This is different from an ordinary class with a static accessor method and a private constructor where the accessor is used to return an instance of the class.

An abstract class is a class which defines some functionality, and optionally some methods that you are expected to provide behaviour for, but the class cannot be instantiated. This means that the class must have a concrete implementation that derives from it to be called.

An interface is a contract. Nothing more, nothing less. It states that your class will provide implementations of certain methods. As such, an interface cannot have items such as method implementations, or field definitions. As you may be aware, C# does not allow you to use multiple inheritance - what you can do though, is have multiple interfaces on a class.