Switching
In the case of switching the transistor is used as an electronic switch. The transistor can turn an electrical circuit on or off, just as in the case with the point-contact transistor and the two lamps. With the left part you could turn on the right lamp.

The difference between a transistor and a mechanical switch is that the transistor doesn't contain any moving parts and therefore doesn't break quite as easily. The transistor is also operated by an electrical current and not by a mechanical force, such as the pushing of a finger. This enables the transistor to switch between on/off much faster than a mechanical one.