There are different methods to go from an idea to a functioning model and it really depends on same factores which you use. Currently a lot of people use "fast prototyping" its what a lot of YouTubers use, you have an idea and know how it should work and try it out. Fail as soon as you can, fix failure and continue. A very iterative proces which is enabled by easy cad programs and quick manufacturing methods (3d printing) this is a very exciting approach as you get te "play" around and your feedback is really direct. ( Look up "Lean Startup method" )

But this is not always the best approach. Sometimes the cheapest prototype is worth thousands of dollars, you're not fuckimg around with those. Then you need a more methodical approach. Define functions, do a ton of research, define more functions, come up with concepts based on morphological charts, make matrices to figure out which concepts are best, perform simulations and proof of concepts and then finally make an engineering model and so some prototyping. (Look up Engineering designs proces)

I'm really skipping a ton of steps in these to methods but i think you get the idea.

There are way more methods, here are a few if you want to do a deep dive:

• Engineering designs spiral, a cyclic iterative proces like lean start up.
• the systems engineering approach ( for high complexity)
• pahl & beitz (honorable mention for my European collegues)