Console Readline

Question

Console.WriteLine("Input the length and breadth");

int a = 10;

Console.WriteLine("Lenght of the rectangle is" + " " + a );

Console.Writeline("Now enter the \"breadth\" of rectangle");

Console.ReadLine();

int b = int.Parse(Console.ReadLine());

int Perimeter = 4*(a*b);

int Area = a*b;

Console.WriteLine("The perimeter of rectangle is" + " "+ Perimeter);

Console.WriteLine("The area of rectangle is" + " " + Area);

First question :

In the above program if i comment out console.readline(); , then i am getting the output.

But, if i dont comment out console.readline();, then i am getting an exception error. Why?

second Question:

When the fourth line of code is executed i.e Console.Writeline("Now enter the \"breadth\" of rectangle"); i am getting a cursor mark to input the value from user. But the same cursor mark is not appearing where there are other console.writeline . Why?

Third question:

I have confusion when we use Console.readline(); What does this do?