These two documents here are one relatively easy introduction to the world of polyrhythms for the piano.
ScalePatterns1 features the right hand varying over a steady left hand, while ScalePatterns2 is the opposite, right hand steady over variable left hand.
Before you attempt any of the two, it is a good idea to play just the phrases of the right hand on ScalePatterns1 just to see how they sound, and how to best play them in time. It is better at first to just play one metronome over the whole bar, so use a very slow metronome to encompass the whole measure.
For any questions, this is the place to ask!