There are several ways to create a new sub-task.

1. To add a Sub-Task to an existing Task in a Tree View, click on the the New Sub-Task icon to the right of the title of the Task you want to add a Sub-Task to.
2. To add a Sub-Task to an existing Task in a List View, click on the the New Sub-Task icon on the row of the Task you want to add a Sub-Task to.
3. If you are in the Edit Screen of a Task, you can click the New Sub-Task Button in the Toolbar.

In all of these cases, you will be taken to the New Task Screen.

Once at the New Task Screen, you can enter the Properties of the new Task. After the fields are filled out appropriately, click the Save Button in the Toolbar. Now the Sub-Task is saved for the designated Task.