Greetings
Like any modern Auto Pilot, you have an outer loop and an inner loop.
Both loops are feed by the FMS when in managed mode, by the Pilot using the FCU when in selected mode.
The outer loop handles a request to change the aircraft C of G position in space, such as turning, climbing, descending
The inner loop will provide how much rotation is required around the aircraft axis to make good the changes requested by the outer loop. In most cases the inner loop is fully managed by the FMS, however as the FMS is dormant between preflight flight phase and THR RED, the FG is then ruling the show and computes and displays through the FD ,the pitch requirements in order to follow the SRS elaborated by one of the FG. functions