3D printing is a prototyping process that enables you (with some effort and patience) to create your prototypes on your desktop, through printing 3d objects from digital models.
Here’s a number of links to a few beginners guides and off course you can always visit the original RepRap Wiki.
1. 3ders – is an indepth resource of 3D printers and a good overview and videos explain aspects of 3D printing
2. Digital trends – A beginners guide to the desktop factory.
3. What is 3D Printing – An overview of 3D printing by Makerblog / ANAT – Australian Network for Art and Technology.