If you have a symmetric quad:

Then EasyTune is one knob that you adjust for best flight, which is just short of oscillation, and that has P, I, and D (roll and pitch) all set correctly from the one knob, as you fly.

In OpTune, you use one knob for TxPID to adjust the P value to where it is oscillating slightly, plug that in to the formula and get P, I, and D values to put in configuration.

If you don't have a symmetric quad, it is a little more complicated for either process.