example of public interface c#

Example: what is inteface and how to use in c#

interface IShape
{
    double X { get; set; }
    double Y { get; set; }
    void Draw();
}

class Square : IShape
{
    private double _mX, _mY;

    public void Draw() { ... }

    public double X 
    { 
        set { _mX = value; }
        get { return _mX; }  
    }

    public double Y 
    {
        set { _mY = value; }
        get { return _mY; }
    }
}