I suppose a 3D printer could be described as similar to any computer printer except its usually much taller to accommodate the 3rd dimension and uses plastic filament in lieu of ink to produce the part. The 3rd axis is the Z which creates the thickness of the part layer by layer with the code output by software called a "slicer" which defines the layers by inputting 3D computer created models.
The filament, which comes in a coil similar to weed-eater string, is fed thru a heated extruder which produces a stream of molten plastic about 1/64" (.4mm) in diameter which is distributed layer by layer with the X and Y axis printer movement.
There are hundreds of thousands of 3D models available for free downloading off the internet but the real creativity comes from learning and using 3D CAD on the computer
sticker maker.