NEED HELP! Arrays Getter and Setter method?

Please see the code below i am having difficulty understanding it.
I am using operator overloading to add two matrix of same size.

public const int size = 3;
int[,] matrix =new int[size,size];

Question1:
//What does the below function do?


public int this[int x, int y]

        {

            get { return matrix[x, y]; }

            set { matrix[x, y] = value; }

        }

Question2:
//why can i not use the name(matrix) to get the values from the array e.g?


public int matrix[int x, int y] //getting error on this

        {

            get { return matrix[x, y]; }

            set { matrix[x, y] = value; }

        }

Question3:
If i comment the below code it gives me error
i.e "Cannot apply indexing with [] to an expression of type".........etc


//public int this[int x, int y]

//        {

//            get { return matrix[x, y]; }

//            set { matrix[x, y] = value; }

//        }

WAITING FOR REPLY?
THANK YOU?

Hello,

Question 1: This is called a property. Properties can be used for many things. Mainly, though, they are used to allow an external class to access a private object. So if you have a private array that you want to use in another class, you make a property that allows you to access it. Another cool feature about properties is that they allow you to make a object read-only, just by removing the "setter". Properties have several other useful features, and I suggest you do a google search to find out more.

Question 2: You cannot make a property that has the same name as another object. So if you have a private array called matrix, you must name the property something else.

Question 3: I cannot answer this without seeing the whole error message or the rest of your code.

Hope this helps!