Transistor questions

I'm kind of a noob to electronics and right now I'm trying to pin down the basics of transistors.

I have a few pretty specific questions, but I'll probably have others as usually one answer excavates other curiosities.

A regular NPN transistor adds up the two inputs voltages correct?

I figure that because that's why they're used for amplification of various, otherwise weak, signals.

If this is true, will the same transistor add up two even voltages from the same source?

Mathematically, it seems impossible. If you have a DC source splitting at the beginning onto two parallels both leading to the ins (I can't remember the terminology -- correct me there too please) and then back out, and directly to the other side of the source, that would mean that it's taking in twice as much voltage as it's putting out, which is, to my understanding, impossible.

Do I misunderstand the basics or... I have no idea. What's the deal here?

Additionally, if you happen to know why/how the transistor does what it does, I'd appreciate those answers as well.

A transistor can be used in 3 different ways.
Usually it uses a small input current to make a large output current.
Resistors convert the current into voltage so a small voltage across a resistor at the input makes a small current that the transistor amplifies into a large current at the output that is converted into a large voltage with a resistor.

A mixer circuit is used to add voltagesa or signals. If two voltages or signals are the same then the output is double the amplitude of one of them.

Hi Galvertez

Check out this link; it's a tutorial on transistors.
**broken link removed**