1990 Toyota Camry Car goes in reverse but not forward

The car had been shaking previously when stepping on gas and accelerating. When driving there seemed to be no issue. It only happened when I came to a stop. I did not know this was a problem, just thought it was cold. My friend looked at the transmission fluid and it is real low. Is this just a low fluid problem? Or is this a leak and what to do if it is a leak? I want to be smart and if the car is going to cost to much to fix, or is not worth the money to fix, I want to get another used car. Thanks