CLEAN : Germanwings co pilot practiced crash descent on earlier flight

The video tutorial discusses an aviation accident involving a flight to Barcelona. It covers the sequence of events, including ATC orders for the aircraft to descend, the flight commander's absence from the cockpit, and the copilot's actions. The copilot, left alone, executed several autopilot commands, repeating actions from the accident flight.

What was the role of the commander during the flight?

How did the copilot's actions relate to the previous accident flight?