A subtask is a useful means to split or break down a task into a number of smaller tasks in order to track each associated activity required for successful completion of the task.
It helps to assign & track it separately to better organize your tasks. It allows each resource to understand their responsibilities.
All the subtasks are linked or related to a parent task. Like a task, OrangeScrum allows you to set priority, % progress, assign to, start and end date and task type for all subtasks.