Assuming that the possible bets are all understood, Roulette is essentially a trivially simple game to play. For each turn, once all bets have been placed using coloured chips to distinguish each player, the croupier halts betting, spins the wheel, and rolls the ball in the opposite direction. When the ball comes to a halt in one of the slots, the croupier announces the result, collects all losing bets and pays out the winner's profits.
On an American wheel, there are 38 spots: numbers 1-36, plus 0 and 00.  Your odds of winning a one-number bet are 37 to 1 (37 ways to lose, 1 way to win).  But if you win, the casino doesn't pay you 37 to 1, they pay you less: 35 to 1.  The difference between the true odds and what they actually pay you is 2/38, or 5.26%.  You can do this same calculation for the other bets, and it comes out the same.