First assistant director in practice
In pre-production the 1st AD breaks down the script and builds the schedule. On set they call for quiet, call the roll, keep the crew moving between setups and are responsible for safety. The 1st AD is not an apprentice director: it is a separate career based on logistics.
Where it lives in CrewDesk
In CrewDesk the first assistant director typically owns the shoot-day events on the calendar and the tasks that must be done before each day.