To determine those values, trial and error often works OK.
It seems like if there are quadrature encoders then the "proper" way to do this is with some sort of a PID algorithm (though usually P is enough)
I certainly agree, but a beginner has to start somewhere. Early on, many are surprised that "identical" motors and wheels or tracks behave differently.
Sad about the "Let's Make Robots" guy. He should be encouraged to post the material elsewhere.
Are you aware that not all the PWM outputs are at the same frequency.For the UNo.pins 5 and 6 PWM Frequency = 62500Hzpins 3, 9, 10, 11 PWM Frequency = 31250Hz
For those of us who were active on the site it was a disaster. Hackaday called it a "kerfuffle".