OOPs...

OOPs or Object Oriented Programming is an approach that puts object at the center of programming model. An object is a self contained entity that has a state and behaviour. State is described by fields and properties, while behavior is defined by methods and events. Object is an instance of a class. 

A class acts like a blueprint for the object. It defines behavior of object of that type.So all objects of type Vehicle will have the same behavior.

Vehicle class will have the properties - 'color' , 'weight', 'model', 'make' . Properties are characteristic shared by all objects of a particular class.  Methods are actions of an object - 'start', 'stop'

Constructors are special kinds of methods, used to initialize objects. It executes automatically when a class is instantiated

Access modifies helps in controlling the visibilty of a class.
* Public allows the property or methods to be called outside the class
* Private fields and methods cannot be used outside the class
* Protected members are accessible from within the class, or any code derived from it

To fully understand the concept, lets consider another example
public class Employee               //class definition
    {
        private string _name ;        // fields

        public Employee()            //constructor
        {
           _name = "Test";
        }

        public AddEmployee()      //method
        {
           //code to add employee
        }
}

Here Employee is a class which is public. We can access all the methods and properties of this class. For convenience we have only created one method and one property, a class may have more than 1.

We can create an instance of this class as follows:
Employee emp1 = new Employee();

Here, emp1 is the object of this class and will have all the features of this class. So emp1 has a name which can be accessed as : emp1.name  Similarly, AddEmployee() method can be accessed using emp1.AddEmployee()

 OOPs helps in modular programming and understanding classes and objects is the 1st step towards it.