"Caching" means that RealFlow | Cinema 4D writes the simulation data to disk (one file per fluid/mesh node and frame) and saves them for later use, e.g. for replaying the simulation or exchange with other programs.
Cache Folder (Mac OS X)
This is the OS X path to the folder where the simulation files will be stored.
Cache Folder (Windows)
This is the Windows path to the folder where the simulation files will be stored.
Use Cache
When enabled RealFlow | Cinema 4D will read existing cache files from the "Cache Folder (Mac OS X | Windows)".
Cache Simulation
When you click on this button RealFlow | Cinema 4D will simulate the adjusted frame range. During this process, particles are not visible, but a progress bar informs you about the simulation's state and with “Cancel” the process is interrupted.
Remove Cache
Be careful with this button, because a click on it will remove all simulation files and empties the cache folder. This action cannot be undone!