Techniques
All digital production techniques are based on CAD drawings. CAD drawings are technical vector drawings with actual measurements. Whether you want to cut something on a laser cutter, or embroider a T shirt, you always need a path that the machine can follow. Vector drawings are line based files while bit map pictures are pixel based files. You can also convert a photo into a vector file by tracing it. On the production side, one can distinguish 2 main techniques in digital production.
Subtractive machining
A milling machine typically cuts away material be it in a 2D or 3D plane. A Laser cutter burns away material be it cutting through the material or by engraving it.
Example: If you want to mill out a square 50 x 50mm in a piece of 18mm plywood, and you got a milling bit of 5mm diameter, you will have to tell the machine to follow your path outside of the line. The cutter area will then be 60 x 60mm, and your square 50 x 50mm. Important to know is that if you want a straight corner on an inside square, you will need to dog bone that corner, meaning milling away the radius that is automatically there from the milling bit. 
Additive machining
A 3D printer adds material layer by layer. It can even add support material for pieces that have an overhang.
Example: If you want to print a square 50 x 50mm x 18mm, the nozzle head will follow your curve inside your path in order to get the measurements right.
There are different techniques in 3D printing. There are pouder based machines which can reach a layer of about 0.02mm recently, and there are other machines who can print over hangs buy building support layers which can be substracted by a lubricant later. There is also "sls" selective laser sinterning, you can print your design in metal! Fablabs cannot provide sls, therefore contact Shpeways or Materialse, the mainframe of 3d printing in europe.
