In plain English, if you want to sense metallic objects, use an inductive sensor. If you want to sense non-metallic objects, select a capacitive sensor.
You asked for it in plain English so here goes..............
Inductive proximity sensors set up a radio frequency field with an oscillator and a coil. The presence of a metal object alters this field and the inductive sensor is able to detect this.
Capacitive Proximity sensors are able to detect the presence of almost any type of material. The capacitive proximity sensor projects a capacitive field in the direction that it is facing. The strength of this field varies with the dielectric constant of the material in front of the sensor. The dielectric constant of most materials varies enough from the dielectric constant of air that the capacitive proximity sensor is able to detect it.
In plain English Inductive for Metal and Capacitive for non metalic sensing !!!!