Emitters are the elements that generate the particles in a simulation based on the settings of each individual emitter item. For the simplest simulation, a radial emitter and a particle simulation item are needed. While this creates particles, in order for the particles to actually render, you need to then create and additional renderable item that uses the particles as a source, such as Blobs, Volumes or Sprites. Geometry can also be applied to particles when utilizing Replicators, providing for a lot of interesting effects.