What is principles of abstraction?

What is principles of abstraction?and what is classes?

In abstraction we hide the irrelevant details (which are not related to concern scenario). We only required object details which are of our concern and will hide the other details to make the model less complex. Classes are user defined data type. We use classes to create objects. For further details please read handout and consult following link: http://forums.asp.net/t/1258933.aspx/1