The prototyping method originally comes from software development. The idea is to get first results very quickly and to receive feedback from the customer on whether your ideas are working. In this way, the software developer avoids having to do major changes once the full solution is developed.
Prototyping in personal development means thinking of the small experiments that you can engage in order to make the first steps towards your goal and to modify your goal early on in case that you have the feeling you are moving into the wrong direction.
Depending on your topic, e.g., developing into a new position, consider one of the following prototypes:
A quick online research on the job profile
A self-reflection on the job asking yourself why you would like to do it and how it will benefit you
Several interviews with people who are currently doing that job, asking them about how they like it and what a typical day looks like
Reading a book about an inspirational person who writes about his/her experience
A one-day job shadowing in your target area
A one-month internship in the area of interest
An (online) course teaching you the basics of the position
What is your current development goal and which kind of prototype will help you to make the first steps?