PROTO is a real-time circuit simulator that allows users to set up circuits with various components and simulate their operation. During the simulation process, users can view various variables such as voltage and current, and check signals on a multi-channel oscilloscope for real-time circuit debugging. The application provides a variety of circuit components such as DC and AC power supplies, resistors, capacitors, transistors, diodes, operational amplifiers, logic gates, sensors, and more, making it an ideal tool for electrician learning and practice.