Creating a prototype or a proof of concept is a critical step in taking your invention to market. To begin, if your invention is simple enough, you can create what is know as a Frankenstein prototype. A Frankenstein prototype is a prototype that is created with whatever you can get your hands on. It is a very rudimentary prototype that demonstrates that your invention works at a basic level. You can use tape, glue, paper, wood, or anything around the household to get your prototype together. Keep in mind, this type of prototype is not "manufacturing ready."
However, to get to a manufacturing ready prototype, you will want to employ the professional services of a product design and development firm. These firms will refine your prototype to make it not only ready for manufacturing but marketable. This is the key word: marketable. The whole point of your invention is to not only help out mankind, but turn a profit while doing so! The product design and development firm will make your product marketable by doing in dept analysis such as color combination, target market analysis, ergonomics and human factors, and will even develop turn your invention into a 3D CAD model with precise measurements and specifications to hand off to a manufacturer to run the initial production.
Another avenue is just to take your idea and sketches straight to the product design and development firm without working on a Frankenstein prototype. Since it is for certain the firm will tweak and redesign aspects of your original design, this choice is a faster route to getting your invention into the market.
In addition to design and development, product design and development firms help inventors source manufacturers either domestic or overseas to handle production for you, help find patent attorneys to protect your invention, as well as a wide variety of services. The job of the product design and development firm is to help take your invention from an idea all the way to placement onto store shelves. This includes marketing and branding services as well as research and field testing if required.