The Grid is commonly used as a container control for the entire page. You normally don't deal with it directly. If you have controls in the grid, you deal with those controls. Give them names(ie.. x:Name="someName"), then deal with the events for those controls. It's almost exactly like WinForms in regards to controls and dealing with events.

For example, here is some XAML from a WPF project(I know it's not Silverlight but basically the same)

XAML
Code:
<Grid x:Name="LayoutRoot">
    <Canvas 
        x:Name="canvas1" 
        Height="100" 
        HorizontalAlignment="Left" 
        Margin="116,62,0,0" 
        VerticalAlignment="Top" 
        Width="200">
            
    </Canvas>
        
    <Button 
        x:Name="btnGetChildren" 
        Content="Get Children" 
        Height="23" 
        Margin="174,209,218,47" 
        Width="75" 
        Click="btnGetChildren_Click" />
</Grid>
Notice that I have a Canvas and a Button "inside" the Grid. Notice that the button has a Click event that I am handling. The code for that click event is in the "xaml.cs" file for the page.