I think the most useful distinction is between randomness and the game's theoretical return. The random-number generator determines outcomes according to the programmed rules, while RTP describes an expected average over a very large number of rounds. It doesn't describe the result somebody should expect from a particular session. The fair-play section of play-nightwin.com explains that its slot results are generated using independently certified RNG technology, which makes it a useful starting point for understanding the process. I also like reading the game's own information about RTP and volatility, since those are separate characteristics. Comparing them helps explain why different slots can have distinct features even when their theoretical returns are similar. For me, understanding the mathematics adds another interesting dimension to game design.