Breadboards are used for testing and experimenting with electronic circuits. I find them extremely convenient because they require absolutely NO soldering, and you just have to plug the component into the little holes that are provided on the breadboard.
Iguana Labs gave a few of these pictures and explanations. Thanks Iguana Labs!
Step 1: The Breadboard Connections
The top and bottom rows (the rows indicated by the blue) and are usually the (+) and (-) power supply holes and these move horizontally across the breadboard, while the holes for the components move vertically Each hole is connected to the many metal strips that are running underneath.
Each wire forms a node. A node is a point in a circuit where two components are connected. Connections between different components are formed by putting their legs in a common node. On the bread board, a node is the row of holes that are connected by the strip of metal underneath.
The long top and bottom row of holes are usually used for power supply connections.