In this paper, we are going to present the finite state machine, how to implement it via hardware description language (HDL), and how to use it in a real application. At first, the specification and requirements of traffic light controller are stated. Then, the system architecture based on finite state machine (FSM) are conducted. Finally, the way of using HDL as well as the test-bench simulation are given in detail. Keywords : Digital system design, System on chip, Finite State Machine, Digital Design Education, Smart Classroom.