My state has a comparative negligence law how does that work and who decides how much I was...

Comparative negligence is where a jury, at a jury trial, can find you partially at fault for the accident. The way it works is that if a jury finds you partially at fault, a judge will reduce the amount of damages at the end of the case by the percentage of your fault. The example I like to give, if you're awarded a million dollars by a jury but found 20 percent at fault, the judge will reduce the damages to $800 thousand dollars.