For the purpose of the ITIL 4 exam, the supplier management practice is the last one you have to remember from the general management section. You need to remember the definition of the purpose of supplier management. The purpose of supplier management is to ensure the organization's suppliers and their performance are managed appropriately to support the provisioning of seamless, quality products, services, and components.
This means that you have to make sure that you have a good relationship with your suppliers, and that way, you can ensure that you're creating these close, collaborative relationships with those key suppliers to uncover and realize new value and reduce your risk of failure. If you rely heavily on a certain person in providing you a service or a supply, you want to make sure you have a good relationship so you know when things might not be working right.
If you have a good relationship with them, they'll be able to come and tell you that what they are running behind so the items they promised to deliver you on a Friday will be delayed and will be delivered instead on a Monday. You would rather have them tell that to you now, so you can plan for that, compared to when Friday comes along, and the thing you expect doesn't arrive and you will have all sorts of problems stemming from it.
By having good relationships, you can be assured that you get better products, more quality products, and better service and supplies. Remember that the purpose of the supplier management practice is to ensure the organization's suppliers and their performance are managed appropriately to support the provision of seamless, quality products, services and components. Keep that in mind for the exam and you'll do great on any supplier management questions.