Red light means cannot turn right. Don't listen to those ignorant people here who create own rules.
Discretionary right turn means the round green light is on (traffic going straight can move) but green right arrow is not on yet. If no oncoming car or adjacent got no pedestrians, you can turn right.

The advantage of this system is it allows traffic from both directions to move, only those turning right must practise discretionary turn or wait for green arrow.

When green arrow is not on and the round red light is on, both traffic going straight and turning right must stop.
In example below, you can only turn right when green arrow is on, because the round red is on. When the green arrow is off (no red arrow here) and red light is on, you must not turn.

This is new regulation that only added in few junction in the past years

Previously descretionary turn can be done on red light