similar to to the one used by meteorology. Instead of forecasting the weather conditions, Astrological predictive system indicates such and such things are highly probable to happen to the people when such and such planetary positions are prevailing.
An analogy is like looking at a colour traffic light system and decoding what each of the colour light such as red , yellow and green are meaning and saying, like if some one goes when the red light is shining he or she is highly prone to be met with an accident or when green light is shining it is highly probable that he or she will have a safe passage.
Stars only indicate your past "Karmas"( or the actions ) and depending on the past actions, the direction of the path of life you are going to take while in the journey, towards the ultimate goal the: "Natural evolution process towards the Perfection of Mind" * "kingdom of heaven", "Moksha", "Nirvana" or where ever according to your personal belief. It is as same as, depending on the lane you have stopped, the direction you should turn will be indicated by a traffic signal.