What is a transistor, how does it work, and how can it be used as an amplifier or switch?

David,

Thanks for asking us about this, we are always happy to help.

A transistor is a 3 terminal device that has one terminal that controls current flow through the other two terminals.

The control of the gate (such as a MOSFET) or base (such as a bipolar) can be either voltage controlled (MOSFET) or current controlled (Bipolar).

Rather than a lengthy explanation of various types and explaining amplifiers I googled a couple of links which are below that provide explanations.

I hope this helps