For a game like roulette, the online casinos will have a live dealer (or sometimes just a live wheel where the ball gets inserted automatically). All your bets are placed on your phone screen but the wheel spins in real life, and then the result is seamlessly digitized, so you're paid out immediately.
While mathematics can help you understand the odds and probabilities of different outcomes in a roulette game, there is no guaranteed way to win using mathematics alone.
You can play a wealth of exciting roulette games at elite online casinos such as BetMGM, Caesars, FanDuel and BetRivers. The best sites offer American roulette, European roulette and French roulette, along with a variety of live dealer options.