Roulette is designed so that the casino has slightly better odds of winning than you do. You might be able to win over the short run (which is why people play the game), but the more you play the more likely it is that you will lose money. Roulette has been designed so that the casino has a slight house edge, which means that over the long run you can expect to lose more than you win. The actual risk is in the game of roulette itself. You can deposit real money, play for real money, and withdraw real money if you win. Yes, there are online roulette casinos you can trust to play at for real money. However, whilst the spinning of the roulette wheel isn't exactly 'real', the results are still random.
So ultimately when you're playing online roulette, you're betting against a random number generator with a pretty interface.
Of course if you're playing live roulette the results of each spin are based on actual physics, but the digital versions of online roulette are simply simulations based on randomly generated numbers.
