system
Given the following post, respond as if you're commenting on Reddit:
human
How do transistors act as amplifiers?

I understand how they can Bernabè like switches, but how do they behave like amplifiers? What exactly do they do to have this characteristic?
gpt
They way they work as switches is essentially the same way they work to amplify.  

There's three wires from a transistor-- the source, the drain, and the gate.  The gate can be thought of as a valve that opens and closes flow from the source to the drain.

When used as a switch, the valve is basically just opened or closed all the way.  Things either flow or don't.

But you don't have to open the valve all the way-- it can be a little open, or halfway, or 80%, or anything in-between open and closed.

Now... imagine that the source is connected to a big power supply.  If you send your small signal to the gate, it opens and closes the valve proportionally to the signal.  If you open the gate 50%, you get 50% of "very big power supply" at the output.  

So you essentially make a much bigger "copy" of the original signal by using that signal to open and close a valve proportionally to the signal, which lets through a much bigger amount of power, and that larger power supply is shaped by opening and closing the valve to come out as an amplified version of the original.