PARTICLE_SYSTEM asset configure a certain type of particle system.
COMP_PARTICLE_EMITTER component is attached to a game object and emit the particle system in the scene.
COMP_PARTICLE_EMITTER_TOGGLE is a particle emitter controller that will just stop and restart the COMP_PARTICLE_EMITTER attached to the same game object when disabled / enabled. It is especially used to control particle system emission during production cycle in workplaces to avoid directly turning on and off the particle emitter, which would lead to instantly hiding the particle effect instead of stopping it.
See mod Example 02 for a complete example.