To create a sub-task of any task you have to create a task first. After creating the task you will get an “Advanced” button. As shown in the below image. Click on that advanced button.
Now select the “Add Sub Task” option from the drop-down.
After selecting the Add Sub Task option you will see a new box where you need to fill the details about your Sub Task.
Click the ” Create ” button and you will see the Sub Task. Always keep in mind that the ID of any Sub Task always starts with “S”.