Having structured your tasks, you need to add your first thoughts on start and end dates for each.
Note that you don’t do this for high level tasks with subtasks. When you made a task a sub-task, the task above (typically a high level task) became a parent. As such it is no longer a task you need to carry out, it is just a container for sub-tasks.
At this point, if you haven’t already, you should rotate your phone to view the graphical schedule. This will enable you to see what your plan actually looks like and – if you need to – to drag tasks to amend dates.