The breadboard lets you build your own circuits with common electronic components. It's a great way to learn about electricity, and to experiment with making your own inventions. Building experimental circuits to design your own projects is called prototyping, and it is a real-world engineering skill.
The breadboard is surrounded on three sides by black sockets. These make it convenient to connect circuits on the breadboard to power, ground, and the Propeller I/O pins. There are also sockets to connect to a digital-to-analog converter and an analog-to-digital converter.
If you have never built circuits on a breadboard before, watch this video about breadboards and how to build circuits on them. History can be pretty interesting!