Oop's concept in short description in c#

Object Oriented Programming:
-Traditional languages like "C" are known to be Procedural languages which doesn't provide the features likes Code Security and Code Re-usability.

-To provide the above features a new approach in programming has been introduced as Object Oriented Approach.

-OOP languages supports security and re-usability, to call a language as object oriented it needs to satisfy the following principles:
 -Abstraction
 -Encapsulation
 -Inheritance
 -Polymorphism

Abstraction: this principles talks about hiding of the complexity by providing the user with a set of interfaces to drive the functionalities.

Encapsulation: this principles talks about wrapping of the code under a container known as "Class" which is going to protect the content inside, as wrappers always protect the content in them.

Inheritance: according to this principles if there is a parent child relationship between any 2 the property of the parent can be acquired by their children, so in the same way if u can establish parent child relationships between classes, the code in 1 class can be consumed in the other, also referred as reusability of the code.

Polymorphism: Entities behaving in different ways depending upon the input they recieve is known as polymorphism, which allows you to give the same name for more than 1 method present in a class.

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Defining methods under a class:
[<modifiers>] <void | type> <Name> ( [<params>] )
{
   <Stmts>;
}

Params are passed as following:
[ref] <type> <var> [,...n]

//No Input & Output
void Test1()
{
   Console.WriteLine("First Method");
}

//No Output Has Input
void Test2(int x)
{
   Console.WriteLine("Second Method: " + x);
}

//No Input Has Output
string Test3()
{
   return "Third Method";
}

//Has Input & Output
string Test4(string name)
{
   return "Hello " + name;
}

//Returns multiple values
int Test5(int x, int y, ref int z)
{
   z = x * y;
   return x + y;
}

a = p.Test5(100, 25, ref b);

<class> <obj> = [ new <class>( [<arglist>] ) ]

Program p;  //p is a variable
p = new Program();  //p is a object
 or
Program p = new Program(); //p is a object

Note: The object of the class in java & .net programming languages gets created only with the use of "new" keyword, if new is not used it is considered as a variable of the class which will not occupy any space in the memory.