For the most part, all graphics you deal with are traditional 2D raster (bitmap style) graphics. While many programs such as GIMP, Photoshop, Paint.NET, etc. are able to combine layers to produce a single image, the result is always a “flat” object. If you want to deal with 3D-esque graphics and manipulation power you get from them, vector graphics is the way to go.

If you are looking to explore vector graphics, give the open source editor Inkscape a look. Inkscape is a powerful editor which gives the ability to fully exploit vector graphics in a standards friendly XML format. There is extensive documentation and tutorials as well as a lengthy FAQ available to get you started. Additionally, you can view a lots of user contributed creations which demonstrate what others are using Inkscape to produce.