What is a Prototype?

A prototype is an early model, or proof of concept, that has been created to test an element of a design. 

A prototype, to be more effective, should only test one function or element of a design, and (ideally) should not be a complete model. For example, a prototype of a phone might be to test the visual appeal of the design of the phone, or the placement of the buttons, by making a mock-up of the phone on a 3D printer! Doing prototypes of individual functions or elements of a device means that each part can be tested properly, and with more precision, and with more focus. This also means that design iterations can be completed faster and without having to recreate the whole thing.

TL;DR? Watch the video!

Why should you use a prototype?

There are many reasons, chief among which is that you can test a certain function of your design! As mentioned above, if you are creating a phone, you can create a prototype to show the button location, in an attempt to test how well people are able to use this button placement, and how appealing it is.

Use the KISS principle: Keep It Simple, Stupid.

Design your prototype to test one design function or element - and make sure that what you are testing is properly defined! It is no use to create a test without knowing what you are testing for. When designing your test 'purpose', try to frame it as a Yes / No question such as "Is the button placement comfortable?" or "Is it visually appealing?". This Yes / No question can then lead to the larger question of "Why?", though having the straight up Yes or No makes collecting data about the prototype so much faster and easier.

Another thing to keep in mind is that you should keep and document all your prototypes. This way, you can look back at the earlier tests, and make sure that your next prototype doesn't create overlap amongst previous prototypes. 

"The definition of insanity is doing the same thing over and over again, but expecting different results" (Unknown, attributed to Einstein)