In this post I show how you can easily add a control to a silverlight grid layout from code behind.
First you draw the grid in the xaml.

    <Grid x:Name="LayoutRoot" Background="Red"> 
        <Grid.RowDefinitions> 
            <RowDefinition Height="20"> 
            </RowDefinition> 
        </Grid.RowDefinitions> 
        <Grid.ColumnDefinitions> 
            <ColumnDefinition Width="300"> 
            </ColumnDefinition> 
        </Grid.ColumnDefinitions> 
    </Grid>

Now in the page constructor add the following code.

        public MainPage()
        {
            InitializeComponent();

            var myButton = new Button
            {
                Name = "btnOk",
                Content = "Ok",

            };

            myButton.SetValue(Grid.RowProperty, 1);
            myButton.SetValue(Grid.ColumnProperty, 1);
            myButton.Click += myButton_Click;

            LayoutRoot.Children.Add(myButton); 
        }

Also add the evento of the button.

        void myButton_Click(object sender, RoutedEventArgs e)
        {

        }

The code needs no comment because it’s very simple.
The only important thing is the method SetValue because it is used to set XAML attribute of element.

For a better understanding I have created an example that you can download from here.