How to add Sub-Task under a Task.

Go to the list of Tasks and hover the mouse over the Task. 

Click on the + button, and it will create a drop-down space under the Task. Type in the Sub-Task name and click enter. 

Once the Sub-Task is created, an arrow will appear in front of the Task name, and a +1 sign will appear after the name.

To edit the Subtask, click on the Sub-Task name or click on the pencil icon.

In the Subtask pop-up window, fill the required details and close the window.