This is a very basic circuit which consists of 2 parts
1st is the noise generator which is the first transistor with no collector connection
2nd is the bit which may look more familiar which is an AC common-emitter amplifier and this is just to bring the noise upto a usable level - I have taken a scope screenshot of what the noise looks like however it is an audible sound which is pretty useful for testing guitar fx or filters and other such things.
if you wish to learn more about the common-emitter amplifier the best source for information is "The Art Of Electronics" book - on page 77 almost the exact same amplifier circuit appears with explanation
you can of course experiment with different types of transistor in the noise section - i'm not sure how available the BC108s are now, I just happened to have a load of old ones, I hit it with a hammer to get a bit more noise out of it.
the best voltage I've found to use this at is 18volts however it does make noise at 9volts upwards