Here's a very common plastic package; the TO-92. Beware, not all parts
in TO-92 share this pinout. Here are some that do:
Common Emitter Configuration
Here the emitter terminal is common to both the input and output signal. The arrangement is the same for a PNP transistor. Used in this way the transistor has the advantages of a medium input impedance, medium output impedance, high voltage gain and high current gain.
Common Base Configuration
Here the base is the common terminal. Used frequently for RF applications, this stage has the following properties. Low input impedance, high output impedance, unity (or less) current gain and high voltage gain.
Common Collector Configuration
This last configuration is also more commonly known as the emitter follower. This is because the input signal applied at the base is "followed" quite closely at the emitter with a voltage gain close to unity. The properties are a high input impedance, a very low output impedance, a unity (or less) voltage gain and a high current gain. This circuit is also used extensively as a "buffer" converting impedances or for feeding or driving long cables or low impedance loads.
A note on Phase Shifts
In both the the common emitter and emitter follower configurations, the input and output signals are out of phase by 180 degrees. This is not a phase displacement, but a phase inversion. The common base mode however tracks the input and output with 0 degrees phase shift.
Transistor / IC / Diode layout.