Particle systems generate large numbers of small elements (particles) — like dots, sparks, or debris — that can be controlled to simulate natural phenomena such as fire, smoke, rain, snow, or magical effects. This lesson covers the basic concept of how particle systems work: an emitter releases particles which then follow rules for movement, lifespan, size, and color, controlled through parameters you can adjust. Tools like CC Particle World and Trapcode Particular (a popular After Effects plugin) are commonly used to create these effects.