Just like we have a 2D printers which prints on paper, we also have this 3D printer which manufactures real world objects
A 3D printer is robot which deposits material on a bed, with the help an extruder, layer by layer as per the CAD (Computer Aided Design) of the object.
Ford engineers send CAD files between facilities, then build prototypes at workstations
using MakerBot Thing-O-Matic 3D printers.
(Source: Ford Motor Co.)
A 3D printer is not only used in industries but is also used by many hobbyist to create 3D printing objects at home, many such ready made designs can be found easily online from thinginverse https://www.thingiverse.com/ which you can use to print objects at home
This iPhone Case is printed with a 3D printer
Another Example is this paper clip
A Toy Boat
Apart from using others designs you can create your own with this open source software
There are many other professional software with the help of which, you can create your own 3d modiling drawing , they are AutoCad, ProEngineer, Catia etc.
You can purchase this 3D printer from http://www.makerbot.com/
They are little expensive but if you are true enthusiastic then you can make your own 3D printer with as little as $300 and with open source hardware and software called RapRap