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To render, add a RenderMan ROP from the RenderMan Shelf. 

If you want to render using Stylized Looks, then you'll need to add a Stylized Looks ROP from the RenderMan shelf.

This tool also creates a RIS Network and sets the integrator to PxrPathTracer.

Make sure the Camera parameter is set to the render camera (you must create one in Houdini as the default cannot be used), then press the Render button to see your render interactively in the Image Tool. See Rendering for more information.