Tags are a top-level method of organization. Tags can be applied to a Task, Heading, List, or Space.
On any view, you can use the Filter Menu to filter that view for specific tags. On views like Today, the tag filters go beyond just specific tags and also account for parent tags. For example, on Today, filtering by the tag “personal” would also include tasks inside of a list with the tag of “personal”, even if that specific task isn’t tagged with “personal”.