The RFFluid node can be created using any of the following procedures:
Toolbar
Clicking on the "RFFluid" button from RealFlow | 3ds Max toolbar.
Menu
Clicking on the "RFFluid" option from RealFlow | 3ds Max menu.
Create panel
Click on the Geometry button and selecting the RealFlow subcategory. Then, click on the "RFFluid" option.
Auto creation
Other RealFlow | 3ds Max nodes like RFEmitters may automatically create and link a RFFluid node for convenience.