|Suggested Tools:||soldering irons, breadboards|
Transistors are three-lead components of electronic logic circuits that only let their input (collector) go through to their output (emitter) if the correct "gate" condition is met. They are basically electronic switches that allow a small amount of electrical current to control a much larger one. 
Shopping tip: to make sure you are buying parts that are fully open at the 5 V gate-source voltage (UGS) a microcontroller can typically supply, try searching for "logic-level gate".
- we could make a simple transistor test circuit as described in this "Make: Projects" entry