What are Subtasks ?
A big Task can be split up into smaller tasks or subtasks. All Subtasks will be mapped under the parent Task. The subtasks can be assigned to different members of the team.
Refer here for more instructions.
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Can I set Due dates/ Reminders for my tasks/ Subtasks?
You can set Due dates and Reminders for your Tasks when you create them. You can also choose to update the details later, by editing the Tasks/ Subtasks. Refer here for more details.