In the Iconography section if the Android Design Guide they describe the following style that should be used for Launcher Icons:
Use a distinct silhouette. Three-dimensional, front view, with a slight perspective as if viewed from above, so that users perceive some depth.
I'd like to know how to create this effect with Inkscape. At the moment I just have a two-dimensional shape and don't know how to continue.
The effect you described is simply achieved by duplicating the shape, changing it to outline, moving it up a bit and putting it in the background.
What the website you linked to describes is a concept of creating a depth perception. The examples you have given are not meant to represent the final design but how this effect is basically executed. The final design should be detailed and represent the function of the app. This is a lot more work than the effect you asked for.