Over on another forum (EEVBLOG), there's a REALLY good thread going on "how transistors work" that is more detailed than "it's an amplifier" and less detailed than "Starting with the state equation of an electron in a quantum well..." In particular, read the posts by "free_electron": How transistors…

How transistors work...

kf2qd May 9, 2012, 9:49pm 9

Bah...

They work on MAGIC! Le the MAGIC SMOKE out and they quit.

So There!