There are the following steps to create visible particles:

  1. Particle system: extra>Particles>Create Part System
  2. Particle type: Create Particle
    • Tips: particles are created randomly between maxsize and minsize, size increment can be positive or negative (should be kept low for a nice effect)
    • Additional: you can set Particle Color, Life, Speed, Gravity and Secondary - just play around with it
  3. Particle emitter: Create Emitter
    • the 4 coordinates are simply the size of your emitter (whole room: xmin: 0, xmax: room_width, ymin: 0, ymax: room_height)
  4. Show particles: Burst from Emitter/Stream from Emitter
    • set the id and number (negative numbers: -5 means a 1/5-chance to spawn a particle)
    • burst: release a load of particles
    • stream: this number of particles will be spawned each step until the emitter is destroyed

Use Destroy actions to destroy emitters or part systems.