The printer creates a molten ABS plastic thread with which you draw the piece line by line and layer by layer.
The design is done in 3D CAD drawing, then exported and loaded into the print program (the slicer)
Then he recorded on a card and loaded into the printer
The consumable is a plastic filament that comes in rolls very affordable prices (20 €/Kg)
There hare many plastic colors and materials, rigid like ABS or PLA (easier to print), elastic, wood like, stone like...
For more info visit http://www.reprap.org/wiki/RepRap_Options
You can also find fully functional printers at affordable prices like XYZprinting Da Vinci 1.0A http://xyzprinting.co.nz/ https://www.youtube.com/watch?v=etAYmwW6H1Q