I’m sorry I cant make you a video. Because I cant edit your CMS
All you have to do is create a new collection related to the topic that you want.
For example, you already have 2 collection with a lot of items. Lets said there’s some category in each item. Just create a new collection (named “Category”, example). Add and Name each item inside “Category” collection based on the category, such as horror, thriller, etc.
Once you’ve done make the “Category” collection. Back to your book collection, and set up reference for each item to the “Category Item”
Hope it will be helpful