In a fluidic amplifier, a fluid supply, which may be air, water, or hydraulic fluid, enters at the bottom.  Pressure applied to the control ports C or C deflects the stream, so that it exits via either port O or O.  The stream entering the control ports may be much weaker than the stream being deflected, so the device has gain.
This basic device can be used to construct other fluidic logic elements, as well  fluidic oscillators that can be used in analogous way as flip flops. Simple systems of digital logic can thus be built.
Fluidic amplifiers typically have bandwidths in the low kilohertz range, so systems built from them are quite slow compared to electronic devices.