How to use tags?
To use tags, first make sure you have them enabled on your Card Template, in board settings.
When you open a card, there will be a Tags field on it. Just type in a tag, hit Enter and exit the card - changes are saved automatically.
A tag that was added to at least one card on the board will become listed in other cards’ Tags dropdown. So, you only need to type the tag contents when it’s not yet present on other cards.
Tags offer a great way to quickly identify tasks by board filtering. You can either type the tag content itself, or preface it with tags: for more accurate results. Complete information about the supported filters & search syntax is available here.
To remove a tag from a card, simply click the small x on it.