Your Library is where you can create, save, and store content - when we say content, this could include destination information, important travel information, company documentation etc. Essentially, any information you need to include in your clients Trips - think of it as your database of information, or content, that you can pull from to add to your Trips.
When you create or add content to your Library, you are creating Documents, and each Document is made up of Pages; this structure helps you keep your content organized. When adding content from your Library into your Trips, you can choose to include an entire Document, or one or more individual Pages - this, again, gives you the flexibility to personalize and customize the information you present to each client.
Advisors are saving destination content and recommendations, packing lists, Visa reminders, contact information and embassy information, agency Terms & Conditions - you can see that the application is broad because you can save any information you want to be able to re-use across Trips!
Essentially, anything that you can think to create can be added as a Document or Page in your Library.