Static resources are declared in Silverlight with the only idea to be reused from multiple places in your code. For example, when you declare a style as a static resource on application level, then this style can be referenced and applied to any control in that application. The syntax when you reference a declared static resource is as follows: {StaticResource resourceName} - where resourceName should be replaced with the name of the declared resource. See the example below:
Xaml
<Button Style="{StaticResource simpleStyle}" x:Name="pushMeButton" Cursor="Hand"></Button>
As you can see the Button's Style property is set to be equal to {StaticResource simpleStyle}. Thus runtime the appropriate style will be taken from the current control's or application's resources and applied to that button. You do not have to specify where the resource should be taken from: whether from the application or from the user control resources.
That's it!