Any note can hold a to-do list. Start a line with the task syntax and it becomes a real checkbox:
- [ ] Book flights
- [ ] Pack
- [x] Renew passport
The - [ ] marker is an open task and - [x] is a done one. There is also a to-do button in the editor toolbar if you prefer not to type it.
Checking things off
Tap or click the checkbox to toggle it. The markdown updates underneath ([ ] becomes [x]), so your tasks stay in sync on every device. Tasks can nest like any list item: indent a task to make it a subtask.
Find your open tasks
The Todo view in the sidebar collects every note that still has unchecked tasks, so nothing slips through.
Completed tasks last
On the iPhone and iPad app and the Mac app, you can turn on Completed tasks last in Settings under Advanced. With it on, checking an item makes it sink below the remaining unchecked ones (bringing its subtasks along), keeping what is left to do at the top. This setting is not available in the web app yet.