PC_and_apple_user originally ask this but reply's are no longer allowed. I found the answer and want to post it because it took me forever to find.
"I am unable to create subtasks for reminders on icloud.com on a PC running windows. The advice of selecting the task then pressing tab does not work. How can I create subtasks on a PC?"
If you want to create a subtask, create a new task under the reminder that you wish to be the parent. Then, click the new reminder so that the color changes, and hit Ctrl+] on the keyboard. This will indent the reminder and make it a subtask of the reminder above it.
I am able to create a subtask by clicking it, and hitting the "Ctrl" and "]" keys at the same time. This makes the task a subtask of the task above. When clicking on the task, it is important not to select it in edit mode. Click the outside edge of the task to select it.
You cannot add a subtask in the tasks edit window. It must be done from the main list page.
It looks like it cannot be done unless on an Apple device? If so, that strikes the app off my list sadly (don't own a Mac, and jumping between PC/Linux and an iDevice just to organise my TODO list is just not going to happen for me).
Subtasks cannot be created at iCloud.com.
That's my experience :(
Creating subtasks in reminders on icloud.com on a PC windows
