The different bets can be categorised generally as outside, inside and announced bets. Bets placed on the Roulette table numbers are inside bets, which usually have lower odds and higher payouts. A wager on any single number is called a straight-up bet and offers a great payout of 35:1.
Outside bets in Roulette are those placed on the special areas marked outside of the numbers. These cover groups of numbers, so you will have an increased chance of winning. However, these increased odds also mean the payouts given are lower than on inside bets.
You can also make special bets called Announced bets when playing online French or European Roulette. There is usually a racetrack to provide quick access to these bets, but you will need to read up on the rules as they can be complicated for beginners.