RenderMan for Houdini is installed using the RenderMan Installer, which manages the downloading, installation and licensing of RenderMan Pro Server (the actual renderer) along with RenderMan for Maya and/or RenderMan for Katana.

After you installed RenderMan Pro Server properly and set up its environment variable $RMANTREE, re-launch Houdini. You are now ready to setup your first scene!

On OSX it may be useful to edit your Houdini.env file like so (being sure the path is the version you're using, below it is 21.0):

RMANTREE=/path/to/RenderManProServer-XX.X
RFHTREE=/path/to/RenderManForHoudini-XX.X
HOUDINI_PATH=$RFHTREE/YY.Y:&

Windows: %HOME%/houdiniX.X/houdini.env
Mac: ~/Library/Preferences/houdini/YY.Y/houdini.env
Linux: ~/houdiniYY.Y/houdini.env