ND = Neutral Density, CPL = Polarizer Multicoated optics minimize reflections, fingerprints and fog/water.
Use the ND4/CPL at dusk or dawn, or on cloudy days, while shooting at 1/250th, and reduce shutter speed by 2 f-stops.
Use the ND8 in cloudy settings while shooting at 1/500th, and reduce shutter speed by 3 f-stops. Use the ND8/CPL in cloudy settings needing polarization, and reduce shutter speed by 3 f-stops.
Use the ND16/CPL in sunny settings needing polarization, and reduce shutter speed by 4 f-stops.
To film the highest quality video from your drone, you want to use lens filters to be able to adjust your shutter speed to double your frame rate. This makes each of your frames crisp and your videos much smoother. Polarization increases color saturation and reduces glare, but should not be used in low light settings or when shooting certain subjects like reflections or shady areas.
The polarized lens filters have an outer portion that rotates freely, so after you attach one to your camera, look through your viewfinder and rotate the lens filter until you see bright objects darken, so you know you have the correct polarization angle.