The MoveToBack and MoveToFront methods can be used to control the order that Layers are drawn. Layers will, by default, draw in the order that they are added to the engine. If you are using Glue, Layers are drawn top-to-bottom. More information on Layer ordering in Glue can be found here.
The following code creates three layers, then moves the first Layer to the "front" so that it is drawn on top of the other two. Without calling MoveToFront, the Layer would be drawn behind the other two as opposed to in front.