How to add contextual filter?

Question

I am working with books in drupal 8. I want to display a specific page("table of contenets") on the sidebar whenever any page of that book is accessed. "table of contents" is a book page. every page of book has two id's.

• page_id
• book_id

Page_id is unique for every page but book id is same for all pages. I believe contextual filter based on book_id might solve my issue. but I don't know how to add contextual filter based on book id.

here are the results of SELECT * FROM book

I can see this "Top level book from current node" . I think this is helpful to do my task. can anybody explain me how can use that option.

Need tons of help.

Thank you!