Keeping a certain heading using a gyro

[KenWittlief]

the simple way to let the gyro steer your robot is to use the single-joystick algorithm for steering

zero the gyro reading as you have already discussed

then use the gyro heading signal as if it were the single-joystick command

if the robot starts going off course the gyro heading will become non-zero, and that error signal is then used to steer the drive train back to the zero heading.