When using the FakeCam script, the selection of layers in your composition plays a crucial role. FakeCam will use as many levels as layers you have selected. The distribution of these layers in a simulated 3D space (Fake3D) is determined by their order in the composition.
The layers at the bottom of your layer stack will be placed further away in the 3D space, while the layers at the top of the stack will be closer to the camera. This creates a multiplane camera effect, giving depth to your 2D composition.
For a visual demonstration of this effect, please refer to this example: