How does 3D printing work

It all starts with making a virtual design of the object you want to create. This virtual design is for instance a CAD (Computer Aided Design) file. This CAD file is created using a 3D modeling application or with a 3D scanner (to copy an existing object). A 3D scanner can make a 3D digital copy of an object.
3D scanners
3D scanners use different technologies to generate a 3D model. Examples are: time-of-flight, structured / modulated light, volumetric scanning and many more.

Recently, companies like Microsoft and Google enabled their hardware to perform 3D scanning, for example Microsoft’s Kinect. In the near future digitising real objects into 3D models will become as easy as taking a picture. Future versions of smartphones will probably have integrated 3D scanners.
Currently, prices of 3D scanners range from expensive professional industrial devices to
$30 DIY scanners anyone can make at home.