Video explanation
Metal contacts press onto germanium while input and output waveforms show a small signal controlling a larger response. The support and test circuit also separate.
Two nearby contacts
The 1947 device used germanium and closely spaced metal contacts, unlike a modern MOSFET.
Control, not energy creation
Input changes conduction so the powered circuit produces a larger output variation. The extra energy comes from the supply.
Bias sets the operating state
DC bias sets a useful amplification region. The gain and waveforms are model outputs, not properties of all transistors.