Inside bets cover individual numbers or small groups of them on the main layout. They include a straight up on one number, a split on two, a street on three, a corner on four and a six line on six. Fewer numbers mean a lower chance of winning and a larger payout. Outside bets, such as red or black, cover large groups and pay less. The house edge is the same for most bets on a given wheel, so inside bets are not better or worse in the long run.
Example
A straight up bet pays 35 to 1. A corner bet on four numbers pays 8 to 1. On a European wheel, both bets carry the same 2.70% house edge.