Pressure advance does two useful things - it reduces ooze during non-extrude moves and it reduces blobbing during cornering. This guide uses the second feature (reducing blobbing during cornering) as a mechanism for tuning.
In order to calibrate pressure advance the printer must be configured and operational as the tuning test involves printing and inspecting a test object.
For detailed information as to how pressure advance operates read https://www.klipper3d.org/Kinematics.html#pressure-advance
For instructions about tuning pressure advance see Orca's calibration tool documented at https://github.com/SoftFever/OrcaSlicer/wiki/pressure-advance-calib