It essentially consists of two metal electrodes separated by a small distance, placed in a reactor.
After avalanche breakdown, the gas becomes electrically conductive due to abundant free electrons.
When visible light is produced, plasma generation can be indirectly observed even with bare eyes.
A variation on capacitively coupled plasma involves isolating one of the electrodes, usually with a capacitor.
These energetic ions are exploited in many microfabrication processes (see reactive-ion etching (RIE)) by placing a substrate on the isolated (self-biased) electrode.