The roulette wheel. A rotating rim carries numbered pockets around its circumference. Numbers alternate red and black in a deliberately non-sequential order, designed to spread high, low, odd and even numbers evenly around the rim. Zero, and on American wheels double zero, is green. The standard single-zero wheel has 37 pockets, the American double-zero wheel has 38, and triple-zero formats have 39.
The ball. Launched against the direction of the rim, it loses energy through friction, clips the deflectors, then drops. Nothing about that sequence is predictable in practice, which is the point.
The roulette table. A rectangular grid reproduces the numbers 1-36 in three columns of twelve, with zero (and 00) at the head. Bets placed inside that grid, on individual numbers or small clusters, are inside bets. Bets placed in the bordered boxes outside the grid, covering colour, parity, ranges, dozens and columns, are outside bets. Chip placement defines the wager: a chip on the line between two numbers is a split, a chip at the intersection of four numbers is a corner, and so on.
The dealer (croupier). The dealer opens betting, closes it, launches the ball, announces the winning number, marks it with the dolly, clears losing chips and pays winners at fixed odds. In a land-based venue, each player is responsible for positioning their own wager correctly on the layout, regardless of whether the dealer or the player physically places the chip.
If you are reading a table diagram for the first time, orient yourself with four zones.