Ranked Multiplayer Point System, how does it work?

How does the point system work in ranked races? How do you get points? Do laps count as points, podium finishes, clean laps, finishing a race? Can you loose points from a race, get negative points? I have done 5 ranked races so far with different results. Been on the podium, top 10, out of the top 10, all clean laps in a race. Every race, at the end it will say you earned xx number of points, then it will have an updated total and I will get negative of so many points, no matter how I do. I always sit a zero points because it takes away all my points at the end of the race, no matter what. So can someone explain how points are awarded and taken away after each race.