Close your Cinema 4D application. Extract the RealFlow | Cinema 4D package and drag the archive's content to the “plugins” folder of your Cinema 4D version. After the installation, start Cinema 4D. The plugin appears under “RealFlow” in Cinema 4D's main menu.
Please note that you need admin rights for changing Cinema 4D's “plugins” folder.
RealFlow | Cinema 4D's macOS installer is localized. Here you can see the German version.
RealFlow | Cinema 4D works with R19!