A prototype will help you get feedback from the tester about what the person likes or dislikes about your idea.
It is a good idea to first create a simple and inexpensive prototype that you can test as quickly as possible. The bottom line is that you should not invest a lot of time and resources on an idea that you are not sure the end user wants.
In addition, a simple prototype makes it easier for the tester to provide feedback and suggestions on what can be improved. An overly beautiful and refined prototype can make it more difficult for the tester to see the possibilities for improvement.
To make a prototype for a digital app
You can create a very simple app prototype with paper and pen. You can let the tester interact directly with the prototype or play a movie that shows how someone uses the app prototype.
To make a prototype for a thing or a place
If your idea is about a concrete physical thing or a place, you can unleash your creativity and make a prototype. Feel free to do it with your team, it's a lot more fun!
Example: Here is a prototype that students made to showcase their ideas for improvement in the city:
A paper prototype can also be good for ideas that do not concern a physical thing or place.
Example: When SOF employees wanted to create a new training on crisis management, they made a pretend version of the training content that they showed to their colleagues. They wanted to see how interested their colleagues were and get feedback on the content of the education. See the prototype here.
To make a prototype for a service or process
If the idea is about a service or work process, you can make a storyboard. It is a short series of pictures with, for example, stick figures, which are there to explain the different steps or the important experiences for the person testing (think like the boxes in a comic book).
A role play can also be a good way to showcase the idea. You and your team can play roles or functions in the service to show how it should work. You can also invite the tester to the role play so that they can get an experience of how the service is meant to work.