My 2002 Audi A3 I was driving I went through an intersection and then when I went to accelerate it wouldn't go but the back tires we're spinning but it will go in reverse just fine what would cause it to do that

 

Based on what you described, your Audi A3 likely has a transmission problem. The forward gears are probably damaged or slipping while reverse still works. Another possibility is a rear differential or axle issue since the back tires are spinning but the car won’t move forward. Driving it in this condition could cause more damage, so it needs to be inspected by a mechanic immediately.