Any line that starts with  [ ] or [x] is a todo list item:
[ ] todo task
[x] done task
You can mark tasks as done/undone by clicking on the corresponding checkboxes to the left.
All todo lists are hierarchical by default. It's enough to add several spaces before  to move todo item into sublevel, like this:
[ ] parent item
space[ ] subitem
You can drag todo items to reorder or change their level. It works even on mobile devices, by the way.
© 2022 Pastukhov