There are many ways to go about creating a physical object from an idea. Depending on the object’s purpose, the choices usually narrow down pretty easily. I will list some of the main options we have, and what they are good for.
If the object you have in mind won’t take too much stress, rapid prototyping with polymers is the way to go, and it’s usually the most common form of bringing an idea to life.
At work, we usually use an Objet 30 printer for most of our prototyping; this is a UV curable resin deposition printer. It basically has a head very similar to your everyday household inkjet, but deposits resin instead. The tray it deposits the resin on moves down as each layer (pass of the heads) gets piled on top of the last layer and a UV light attached to the heads cures the resin to a certain degree with every pass.
The results are pretty amazing as far as accuracy, and the material properties are good enough for general testing/use. We use them for general model representations, light/medium stress fixtures.
Stereolithography is like a "pool" of resin that gets cured at the very top. A plate moves each consecutive cured layer deeper in the pool, and the top layer gets cured as well. This process continues and is in essence a type of extrusion of cured resin.
The results are good, not as close as fused deposition, but acceptable. The advantage of this method is a wider variety of materials that approximate physical properties of real polymers. We use them for working model prototypes.
Selective laser sintering melts and bonds each powdered layer into shape. Much like the SLA principal, it extrudes the layers down.
The results are strong parts. The advantage of this method is that you may introduce a material fill/mix into your model, such as glass fibers, aluminum, carbon fibers, etc. We use these models for heavy fixtures.
You may choose this option if you’d like a larger quantity of objects. The initial cost for the mold is a bit more, but each consecutive part is far cheaper.
Depending on your physical object requirements, it may be necessary to have a part CNC milled, sintered and finished (via SLS), or formed with metal material.
The resulting parts are very accurate, very strong, but very expensive. We only use this for large fixtures.