The definitive book for international foxtrot is the ISTD “The Ballroom Technique”. You can buy the book from the ISTD international bookstore for £14 (about $30) https://shop.istd.org/product/item-the-ballroom-technique/ The US-ISTD also has the book for $30 https://usistd.org/manuals-show_wp_shopping_cart/ . The book is invaluable and covers waltz, foxtrot, quickstep & tango. Can not emphasize strongly enough how important this book is to anyone interested in learning (about) these dances. You will probably need professional instruction to help you understand how to understand them; we did.