You can find some great books on braiding and knot work at hought.com
I would recommend “The Art of Braiding, the Basics Revised Addition” for the beginner.
The books consist of detailed photographs, directions and make for a great reference.
At y-knotlace.com you will find the Marlinspike videos by Robert Black.
A good video to start with is Decorative Knotting & Braiding in Leather. You will get step-by-step
directions that are easy to follow. He will also teach some basic knot tying skills. These skills
will be useful for dog leads and a variety of other projects.
Knottactical has some fantastic youtube videos to help you learn knot tying.
Leads N Leather also has a Youtube channel with helpful videos https://www.youtube.com/@leadsnleather
If you already know how to braid in the round this is a very helpful group. Facebook Group Kangaroo Lead Making Mentorships and Supplies https://www.facebook.com/groups/4098773016841375
Facebook page www.facebook.com/leadsnleather
Instagram page www.instagram.com/leadsnleather