Prototyping involves creating representations of design ideas in various forms like physical mockups, video simulations, or paper prototypes. There are two main types - low-fidelity prototypes using inexpensive materials for early testing, and high-fidelity prototypes that more closely resemble the final product for technical and usability testing. User testing of prototypes is important for gathering feedback to improve designs and evaluate alternatives through methods like usability testing, field studies, and expert evaluation. Effective evaluation requires determining goals, questions to be answered, appropriate techniques, and addressing practical and ethical considerations.