As you can already guess by the word, the tool prototyping, in essence, comes down to creating different prototypes. Prototypes can be very helpful for design teams to test their concept or product with clients and end-users. The tangible realization of the product-to-be functions as a conversation piece and makes it easier for the client/user to state his opinion and to reflect in more detail on the aspects he does appreciate and the aspects that still need attention and improvement. By using prototypes the dialogue between the researcher/developer on the one hand and the clients or users on the other hand can be made more productive.
Prototyping can be applied in many cases and in many different ways. You can choose to develop low-fidelity prototypes and high-fidelity prototyping, and everything in between. Just make sure that you know beforehand what you would like to test and in which phase.