These transistors are electronic components ideal for switching circuits and can also be used as an amplifier.
The transistor is a circuit element that can be used as an electrically operated switch. It is made of semiconductor materials, has three terminals and can interrupt or close the circuit between two terminals depending on the command applied to the control pin.
Use with Arduino
There are two common types of transistors: bipolar and field-effect.
The picture shows the symbol bipolar transistor (left) and an illustration of a universal transistor (right). There are two types of transistors: NPN and PNP (depending on the type of semiconductor material). Its terminals are: B - Base C - Collector E - Emitor
The base will be used to control the transistor. Initially, this will not stream (between C and E). If the voltage base - emitter opening exceeds a threshold (about 0.65 V), it will absorb the current through the base and it will let through (almost) freely between C and E.