This is another one of those that looks fearsome but isn't. X1 and X2 are the signal terminals, and usually consist of PCB mounted terminal blocks. Between pins 1 & 8 we find a 10 uF capacitor in series with a potentiometer acting as a rheostat. This allows a variable gain from 20 to 200. The maximum output should be about 46 dB.
You'll notice that the DC supply voltage is in parallel with a capacitor, C1. This is to alleviate any buzzing or distortion caused by the supply voltage. In addition, if there is any stray AC in the circuit, it finds an easy path to ground through C1 and does not enter the amplifier.
The output is taken from pin 5 via capacitor C3 which is there to match impedance between speaker and amplifier. C6 and R2 provide a bypass and bias which improves the tone quality of the output.
At pin 7 C5 provides an easy path to ground, and this is there to prevent any howl round in the amplifier. It is not always necessary.
Parts and values are:
C1 & C2 electrolytic 10 uF (watch the polarity)
C3 electrolytic 100 uF (experiment with a 220 uF and see what happens)
C4 & C5 100nF
R1 preset 10k max
R2 10 ohms
and an 8 ohm loudspeaker rated at 0.5W or more. (Don't use 0.25W as it will end badly).
Supply voltage must be 4.5V min, 7.5 is good and 9V a typical. After this it can get a bit twitchy, although in theory you could feed 15V through there. 9V is more than enough to give a loud clear sound from a portable radio. A volume control can be fashioned by placing a potentiometer acting as a voltage divider before point X1. Use a logarithmic rather than a linear one.