Tasks tab
On Home or a project, the Tasks tab lists Docs added to Tasks under that surface. Use New Task to create one. An empty list shows No tasks yet. Search with Search tasks.
Add an existing Doc
Right-click a Doc and choose Add to Tasks or Move to Tasks. Status options include Not Started, In Progress, Next, Hold, Complete, and others you can customize in Properties.
Island Tasks
The island Tasks button lists Docs with status In Progress or Next. A dot appears when something is active. Opening a row takes you to that Doc.
To-dos in Notes
Layout items of type to-do live in Notes. They can link to a Doc and pick up its status. Use them for checklists inside a page; use the Tasks tab for Docs you want in the island list.