Rotator applies rotations in the order yaw-pitch-roll.
The identity rotation for a car (i.e. P=Y=R=0) corresponds to the car being upright with its nose pointing towards the positive x-axis. If the car were at the center of the field, its nose would face towards the left mid-boost, from the blue team's perspective.
Example: to get a car facing straight up, wheels toward the orange goal, you could yaw 90 degrees right, then pitch up 90 degrees. This corresponds to P=16383, Y=16383, R=0. You could also yaw 90 degrees left, pitch 90 degrees up, then roll 180 degrees. This corresponds to P=16383, Y=-16384, R=32767.