Is there anywhere that explains better the operation of wideband control ?

Press F1 under Closed loop lambda or see brief guide below
Select target map from cal switches
Then setup bank allocation down in engine config if on an Impreza all cylinders should be set to bank 1..
Then setup you target table and also the allowable trims for min max and at full throttle.
After this setup lambda trims for ect and egt and disable thresholds for transient fueling.
Best way to setup the lambda control is by service interval based Intergral gain under gain control.
This then allows you to service the Intergral gain based on time at different loads and rpm. Reason this is wise is due to exhaust gas speeds varying in the time it take gas to hit sensor from port.
To best set this up, log lam1 and fuelfinal1. Then at idle, cruise and full throttle around 3k and 5k make a step change on the fueling to richer mixture and see how long it takes the lambda to see change after fuel final has adjusted. Then populate the service interval calibration.
After this it is a case of logging lambda error and setting up the P and I of the control.
 Q)  Does the lambda simply operate in the background only ? With any active trims only available via logging?
That’s correct, fuelmltcll1 is the trim correction. You can view this live in software by gauge – add and then view how you want and speed you like.
Or log it.
I generally view live when not doing full throttle runs and then load cell hold on Dyno and just multiply the cell by lambda correction to get fuel table right.