We don't currently have the ability to tag/label a page in Tettra yet.
We believe that really really good search is a better experience than having to maintain a tagging system.
If you do want to have tags, you can add them manually. Here is an example with a tag section on a page, this is then easily searchable for any of the keywords:
If you're interested in this feature, get in touch by starting a chat and we can keep you updated on any future progress.