Library Link is a Quest Portal Pro Subscription feature.
When interacting with the AI Assistant you will often see citations at the end of a response. These are links to the sources the Assistant used to create its answers.
If you click on the citation, then it will open the Library to the specific page it used when generating it's answer.
Best Use Suggestion: When you create a campaign, you can set your campaign to a specific game system. This directs the AI Assistant to use those sources as the basis for coming up with answers - this allows a more specific response instead of a general one.
Example: If the campaign is set to Dungeons & Dragons 5e (2014), the Library Link will allow the AI Assistant to pull from the Dungeons & Dragons 5e (2014) SRD instead of giving a potentially inaccurate general rpg answer.