links I read through on resistors:
http://en.wikipedia.org/wiki/Transistor
http://www.williamson-labs.com/480_xtor.htm
What I've surmised from the links:
Transistors are used to amplify signal, they switch between terminals. They are in many integrated circuits. It is an electronically controlled switch that uses a small amount of power to connect a larger flow of power.
555 timers: So they are integrated circuits, basically pulsing a signal