A .rism file is a Rapid Insight Scoring Model. This is a model that has been memorized and has been saved so that it can be shown to others or scored against an original dataset.
A .riax is a Rapid Insight Analysis. A saved analysis can be made up of one or several memorized models
To save as a .rism select Memorize Model > Save Icon
To save as a .riax select File > Save As