while i also wont be chiming in much, here is the explination for a transistor that finally stuck for me
"a transistor is a current amplifier, what ever current you feed into its base, multiply it by its hfe/beta, and that is the current it will allow to flow through, should external components limit the current flow possible to less than what the amplified flow would be, the transistor becomes known as saturated"
now this description isn't absolutly 100% correct, but it helps to understand the concept and how they are used in circuits,
personally i would probably reccomend one of the motorola power supply handbooks, as they went a far bit furthur into how to use transistors, mosfets and op amps in regulation and amplification loops than i expected,