C# How to create different class instance according to my request

This is not a good question - we cannot work out from that little what you are trying to do.
Remember that we can't see your screen, access your HDD, or read your mind.
Creating a class instance in a function is simple:
MyClass mc = new MyClass();
So you need to explain exactly what is giving you difficulties.
Use the "Improve question" widget to edit your question and provide better information.