If you want to do image compositing, layers, collages, you will be better of with Photoshop. The adjustment tools in Aperture are great for developing a photo, raw processing, adjusting intensity, colour, sharpness, retouching minor defects, but Aperture is not designed to create compositions from images. For this, it provides an interface to use external image editors, like Photoshop.
You can import images with layers into Aperture, to manage and store them, but you cannot edit the layers. You can print photobooks from Aperture with a custom page layout, and this way arrange pages with arbitray photos, but this could be more easily done with Pages.