Confusing " openFileDialog.FileOk += openFileDialogFileOk;" statement

In the following example I'm confused about what is occurring with the highlighted statement.  Everything works fine but I just don't get what is going on here with the compound assignment.

Thanks for your help.

John

public MainWindow()

       {

           InitializeComponent();

           openFileDialog = new OpenFileDialog();

           openFileDialog.FileOk += openFileDialogFileOk;

       }

       private void openFileClick(object sender, RoutedEventArgs e)

       {

           openFileDialog.ShowDialog();

       }

       private void openFileDialogFileOk(object sender, System.ComponentModel.CancelEventArgs e)

       {

           string fullPathname = openFileDialog.FileName;

           FileInfo src = new FileInfo(fullPathname);

           fileName.Text = src.FullName;

           TextReader reader = src.OpenText();

           displayData(reader);

       }

       private void displayData(TextReader reader)

       {

           // TODO: add while loop here

       }

   }

}

I don't understand what is happening in the highlighted line of code.

What is being added toopenFileDialog.FileOk?

openFileDialog.FileOk is the event when user clicks "OK", what I don't understand is

What happens with the statement:openFileDialog.FileOk += openFileDialogFileOk; What is being added to what?

 openFileDialogFileOk is a method with a no return value (void). I understand what is happening inside this method, just not the one line of code highlighted.