Have you read your owner's manual? It has a nice description of the function of the ASR system.
In brief, if the system detects wheel spin, it either closes the throttle or applies the brakes, depending on what speed you are going at the time.
The light you saw come on -- are you talking about the yellow triangle in the center of the speedo, which indicates you're on a slippery surface? Or are you talking about the ASR malfunction light?