These resources are not requirements. They are simply suggestions for those who may want to explore coaching in greater depth.
This is the website of the largest and most globally recognized professional organization for coaches
This is the classic book written by the founders of the Coaches Training Institute. It includes a solid guide to coaching philosophy, listening, and other coaching skills.
Co-Active Coaching, Fourth Edition
This book is written by coaching thought leader Michael Bungay Stanier. It is intended for managers or others who will not officially coach but who will have coach type conversations. It is helpful for those who do not want a formal coaching practice but want to be able to transport coaching tools into their own line of work.
The Coaching Habit: Say Less, Ask More & Change the Way You Lead Forever