Welcome to the forum @traceyli!
Tasks have windows that dictate when they are rendered to a user.
Lets say there’s a task that needs to be completed by 30th September but you want to start showing it to the user on 25th September and continue showing it until 5th October (in case they don’t get it done by 30th).
In this case:
dueDate = 30th September
startDate = 25th September
endDate = 5th October