Type the number sign (#), then type a word—for example, #meeting or #important—or choose from the list of suggested tags.
Note: Suggested tags appear if you’ve already added tags in Notes or Reminders.
You can type the tag anywhere in a note. Tags must be a single word, but you can use hyphens and underscores (for example, #meeting-minutes or #important_documents).
Click OK.
Tags you add appear in the Tags section at the bottom of the sidebar.
If you add a tag to a shared note, it appears as dimmed text to other participants who don’t have the tag. They can Control-click the tag, then choose Add to Tags.
Go to the Notes app Sort and pin notes on Mac