The wheel and the ball
A standard roulette wheel is a bowl with numbered, coloured pockets arranged around the inside edge. The croupier — or the game's RNG in digital versions — releases a small ball that spins in the opposite direction. When momentum drops, the ball settles into one pocket, producing the round's result.
The numbers on the wheel are not in sequential order. They are arranged specifically to alternate high and low values, and mix the colours. That layout is intentional and the same on every standard wheel of a given type. Knowing this stops you wasting time looking for patterns in the arrangement.
In an online version on topph, the RNG determines the outcome before the animation plays out. The visual spin is a representation of the result, not the process generating it. Every round is independent — the wheel has no memory of prior spins.