A program to recognize and reward our most engaged community members
I would suggest you watch these getting started videos. They go over model building and scoring, which is what you're trying to do here.
https://rapidminer.com/training/videos/
Of course, if the function to generate z directly from x and y is known, then this can be done simply using a Generate Attributes operator, which supports most common mathematical functions. Otherwise, as @Thomas_Ott said, you are going to have to delve into the world of predictive modeling.
