When you develop a project, it often needs to make IO expansion.The 74HC595 shifting register is a good choice. Following will introduce you that use two pieces 74HC595 to realize the display system of four digital LED(of course, can also realize 8 digital LED display) .It only uses three IO (PIN2,3, 5) of Arduino.
1. ICStation UNO development board $12.69 ( Or Arduino UNO development board)
3.DuPont line: 30PCS
4.four digital LED display with the same anode
5. 20 PCS 20mm pin header
8.4PCS 47Ω resistance