The NPN Transistor acts as a switch or amplifier. With no current at the base, there will be no current flow from collector to emitter. However, a small amount of current to the base will allow a large current to flow through the collector and emitter.
The Blinker module turns a direct current input into a square wave output, allowing you to make LEDs blink and Buzzers beep. It has a green LED flashing in time with the output and a red LED to indicate if power is connected the wrong way. You can change the blinking rate by turning the wheel!
The Buzzer module plays a 4kHz tone. The volume of the buzzer can be adjusted by changing the the amount of power running through it. The plus and minus signs indicate the direction in which it operates.