Object not Instantiated, How can I use its value in the method?

In the C# Objects Video, the teacher creates the OnMap() method inside of the Map Class. I understand how a Point variable can be passed in, and it returns a bool value.

Why can you use the Width and Height values in the method like that? Since the method is written in the Class Map (and I know why he is writing the method) I know that the Width and Height variables in the method are both properties of the Map Class. OK

But they are not instantiated. Since there is not specific object created, they hold no value. I thought that the Class is like the 'Blue Print', even if there was a Map Object(holding a value for Width and Height, how would the method know which instance of Map its referring to?

Sorry if this is a dumb question, working hard to get my head around this concept

namespace TreehouseDefense
{

  class Map
  {

    public readonly int Width;
    public readonly int Height;

    public Map(int width, int height)
    { 
    Width =width;
    Height = height;


    }

    public bool OnMap(Point point)
    {
      return point.X >= 0 && point.X < Width && point.Y >= 0 && point.Y < Height;
    }

  }



}