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 MEGA 2560 is designed for more complex projects. With 54 digital I/O pins, 16 analog inputs and a larger space for your sketch it is the recommended board for 3D printers and robotics projects. This gives your projects plenty of room and opportunities.