A green rating between 7 and 10 indicates good quality surf, based on a long swell period, little or no wind, and swell height greater than a metre. If the wind is quite strong, then it will be an offshore wind.
An orange rating between 4 and 6 indicates reasonable surf conditions, although possibly affected by light-fair onshore winds, and a lower swell period e.g. 8-10 seconds.
A red rating between 1 and 3 suggests poor conditions such as strong onshore winds, a low swell period and a small swell height, all of which can make surfing more difficult.