This is called the Minimum Viable Product, or MVP.
This process is called rapid prototyping. You will use simple materials (like paper and pen) to make the idea you have in your head more tangible. Rapid prototypes are really useful because they don’t typically require a lot of money or time to make. Rapid prototypes are also useful because they can help you better describe the idea you have in your head. Now, let's go build some stuff!