Hows does a transistor amplify sound?

[whcirobotics]

Hi CD,

I am working on my physics report and i am doing it on Transistors. I have tried A LOT of websites, including youtube, wiki, howstuffworks, and even the teacher. Even he does not completely understand it. My last and hopefully best resource is CD. Can someone please explain in the simplest form you can,because i need to present this and my teacher is likely to ask me hard questions on this topic.

What i understand so far:
There are three parts
(1) Base
==> Which the small current comes in
(2) Emitter
==> Can either be input or output(but depending on what?)
(3) Collector
==> Can only be output.

My question is:
How does it actually amplify? What happens?
ALSO
How does it turn on or off?
==> Some websites said that if current is put through the BASE and is higher than 5V then collector opens and it is ON
==> Or if current is put through BASE and is lowest than 5V then collector does not open and it is OFF
P.S. Is this accurate>?

If someone can please help me out on this. I am having some serious troubles, I have tried sooo many websites and i do not get it. Please help me my report and presentation is Monday Thanks in advance.