Activating a story means it will be included in the sitemap, RSS, API and meta information is added so Google can index it. The Sitemap and RSS belonging to a Newsroom Studio account can be found under Domain & hosting > Feeds and discoverability.
To activate a story go to Settings > Properties Tab and turn ON the toggle.
The 'Activate' toggle is linked to the scheduling tool thus making possible the following scenarios:
1. Publish date is in the future, story is inactive. This means the story cannot be indexed by Google.
2. Publish date is in the future, story is active. In this case the story will become indexable when the date is reached.
3. Publish date is in the past, story is inactive. Although the publish date was reached, the story is not indexable.
4. Publish date is in the past, story is active. The story became visible and indexable on that specific date.
There's an additional option at account level - Domain & hosting > Feeds and discoverability - this allows adding the noindex meta tag even if the story is active. The default for active stories is that they become discoverable to Google.