You can preview your render interactively via RenderMan's Image Tool or Render View.
Set Display Device to "it" (the default)
Go to Render View. Select your output, e.g. /out/ris1. And press Render from inside the window.
To render to disk, simply change the Display Device to a file type, such as OpenEXR. Press the Render button. The default RIB type is binary and cannot be hand edited. You can change this in the ROP node Options | RIB