Each icon represents one of RealFlow’s object groups. The order is:
Grid fluid elements
Particle emitters
Daemons
Objects
Meshes
Cameras
RealWave elements
IDOC elements
Clicking on an icon will open a list of all available elements. Choosing the desired object from one of the lists, also places the item in your scene. You can repeat this process as often as needed. Please bear in mind that some elements cannot interact with each other or contribute to a simulation, although they can coexist in a scene, for example RealWaves and grid fluids, or particle emitters and grid fluids.