I studied transistors as a teenager and from what I remember, it's a 3 wire gadget where one wire is for the control voltage which is a very small current. The 2nd wire is for a higher voltage. The 3rd wire is a common wire for both, which is also the output wire from the transistor.
If no current flows in the control wire, then no current flows through the 2nd wire to the output. When current flows through the control wire, the transistor causes a copy of that current to flow through the 2nd wire to the output wire, but at a much higher voltage, thereby causing amplification.
