What is the difference between Reference type and ref in C#?

Question

In both ref type and Reference type I am able to change the value of the object so what is the difference between them?

Someone has provided an answer but it's still unclear for me.

static void Main(string[] args)
{
    myclass o1 = new myclass(4,5);
    Console.WriteLine("value of i={0} and j={1}", o1.i, o1.j); //o/p=4,5

    o1.exaple(ref o1.i, ref o1.j);    //Ref type calling
    Console.WriteLine("value of i={0} and j={1}", o1.i, o1.j);// o/p=2,3
    myclass o2 = o1;
    Console.WriteLine("value of i={0} and j={1}", o2.i, o2.j);  // o/p 2,3
    o1.i = 100;
    o1.j = 200;
    Console.WriteLine("value of i={0} and j={1}", o1.i, o1.j);  //o/p=100,200
    Console.WriteLine("value of i={0} and j={1}", o2.i, o2.j); //o/p=100,200
    Console.ReadKey();
}

public class myclass
{
    public int i;
    public int j;

    public myclass(int x,int y)
    {
        i = x;
        j = y;
    }
    public void exaple(ref int a,ref int b) //ref type
    {
        a = 2;
        b = 3;
    }
}

Answer 1

Parameter with ref keyword provide reference to reference of the object where you can change where this reference will point after changes

public void TestObject(Person person)
{ 
    person = new Person { Name = "Two" };
}

public void TestObjectByRef(ref Person person)
{ 
    person = new Person { Name = "Two" };
}

Then when you use those methods

var person = new Person { name = "One" };

TestObject(person);
Console.WriteLine(person.Name); // will print One

TestObjectByRef(ref person);
Console.WriteLine(person.Name); // will print Two

Below a quatation from MSDN: https://msdn.microsoft.com/en-us/library/14akc2c7.aspx

The ref keyword causes an argument to be passed by reference, not by value. The effect of passing by reference is that any change to the parameter in the called method is reflected in the calling method. For example, if the caller passes a local variable expression or an array element access expression, and the called method replaces the object to which the ref parameter refers, then the caller’s local variable or the array element now refer to the new object.

When you passing reference type as parameter to the method without ref keyword the reference to the object passed as the copy. You can change values(properties) of the object, but if you set it to reference another object it will not affect original reference.