What the traffic rules regarding amber traffic lights?

By "amber" I assume you mean yellow. A yellow traffic light indicates that your "right of way" is ending within the next couple seconds. When the light turns yellow you shouldn't enter the intersection if you haven't already, unless you've reached "The point of no return". It's not illegal to go through the intersection while the traffic light is yellow, but if you can stop you should, if you can't stop then go through the intersection (determined by your own judgement). A yellow light is basically a warning of a red light coming, where it is illegal to proceed through the intersection.

The duration of a yellow light depends on the road the traffic light is governing. For a side road the traffic light may only show a yellow for around 3 seconds, for a major road such as a state road or US Highway, the traffic light may show a yellow for 4-6 seconds. These timings all depend on the road that the traffic light is governing and what the speed limit is for that road.