Mobile app prototypes are interactive mockups of planned digital products, serving as blueprints for developers, outlines for investors, and tools for initial user testing. They help visualize ideas, align teams on UI/UX, validate concepts, reduce technical debt, and provide valuable feedback from users. Creating a prototype involves researching user needs, identifying core features, sketching the app's architecture, choosing a prototyping tool, building the prototype, and testing it with users or investors. Building functional prototypes can lead to more valuable user testing and faster growth of an audience and funding opportunities.