XMB picks up the XSS goal for the day from XATA Training page or the XFAI daily goal.
If a workout is assigned to Planner the XSS goal reflects that workout.
If you want to do your own thing, Like 
selected workouts from the Xert library, or import your favorite workouts and Like them, then assign those workouts to days on the Planner.
- Magic Buckets – The Evolution of the Workout – Xert
- Some helpful Magic Buckets guidance from Smart Bike Trainers - General - Xert Community Forum
An in-depth video from Xert Training Academy is pending.