Transistors as Amplifiers
There are three basic configurations that you can use a transistor in :-
Common Emitter - good gain (but inverting), low impedance in, medium impedance out.
Common Collector - no voltage gain, high current gain, high impedance in, low impedance out.
Common Base - good voltage gain, no current gain, low impedance in, medium impedance out.
The common emitter circuit is the one you will see most of because of its gain.
Common collector (also called emitter follower) is very good at driving low impedance loads (loudspeakers).
Common base is rare unless you play with high frequencies (MHz).
If you look at the circuit inside an integrated circuit (linear or logic) you will see the majority of the transistors fall into one of these categories - there are a few 'cheats' though- connecting transistors backwards for such tricks as using a base-emitter junction as a zener diode or inter-electrode capacitance being exploited.
Stick to the first two and you won't go far wrong!