After adding and setting up shadow casts in Action, you can output the shadow by itself, or as part of your overall composition. A shadow pass is a white image with greyscale regions that represent the shadow coverage. See for information on the specific shadow output settings.
3D shadows have a specific oversampling factor in their UI. Jitter on 3D shadows is inherent to the shadow map technique. However in most situations it can be go completely unnoticed. Some lighting situations which would cause stetched shadows (lights close to the horizon) are very likely to create very visible jittering.
To aleviate the jittering, the factors to look at are:
the resolution of the shadow map itself: in a situation where the shadow gets stretched a lot you need to crank it up (max 2K). Then there is the oversampling factor (it's a specific Anti-Aliasing for 3D shadows). It works in a very similar way to software AA in Action, and also features a softness control. High samples and softness > 1.0 will help conceal water down the jittering effect.
Those options can tax the system quite a bit, and it is a good idea to activate adaptive degradation in order not to slow down the interactive performance too much.