When a design thinker needs to gain insights into the process, he has to carry out some prototypes. The process of creating prototypes comprises an early, economical, and basic version of the product to identify the problems with the current design. Prototyping brings forth the opportunity for the designers to breathe life into their ideas, test how practical the design is, and potentially investigate how the users feel and think about the product.
If you are designing an app, you might start with creating a digital prototype, and introduce it to real users before getting the actual process started. There is no specific shape or size of any prototype, spanning from paper models to full-fledged interactive digital prototypes. Prototyping is done for many reasons, some of which are: