OOPS Concepts 

Class: It is a collection of objects.

Object: It is a real time entity.

An object can be considered a "thing" that can perform a set of related activities. The set of activities that the object performs defines the object's behavior. For example, the hand can grip something or a Student(object) can give the name or address. In pure OOP terms, an object is an instance of a class 

Class is composed of three things name, attributes, and operations

public class student
{
}
student objstudent=new student (); 

According to the above sample, we can say that Student object, named objstudent, has created out of the student class.

In the real world, you will often find many individual objects all of the same kind. As an example, there may be thousands of other cars in existence, all of the same make and model. Each car has built from the same blueprint. In object-oriented terms, we say that the car is an instance of the class of objects known as the car. In the software world, though you may not have realized it, you have already used classes. For example, the Textbox control, you always used, is made out of the Textbox class, which defines its appearance and capabilities. Each time you drag a Textbox control, you are actually creating a new instance of the Textbox class.