Heat sink* improves transistor heat dissipation. This part may help if your transistor gets too hot during experimentation. However, it may not solve this problem completely. If your transistor gets too hot you may also need to decrease the voltage and/or find and eliminate the cause of overheating.
Generally if you experiment with voltages up to 6 Volts you do not need to add a heat sink.
You will need to find a small screw and a nut to attach a transistor to the heat sink. Screw it tightly to provide an easy distribution of the transistor heat to the surface of the heat sink.
* Other types of heat sinks may be supplied.