I found this one good training in Youtube for SAP MM Training, It's quite complete and interesting and thanks to the author who prepared it.

The video covers, The are various authors that I have included the link below which you might want to explore. For those whom want to explore SAP MM, it's never too late to start from youtube video or from SAP Help menu to get started.

SAP Material Management topic is very intersting. Even Udemy also have some knowledge corner about SAP MM on S/4 Hana

Learn SAP MM With Functional Changes in S/4 HANA

1. Overview of Procurement

2. Procurement Process

Basic Procurement

Basic procurement is the process of acquiring goods or services in the right quantity, at the right price, and at the right time. However, it is critical to maintaining the right balance between quantity, price, and time. You can read more by clicking the link

3. Procurement Cycle

Creating Purchase Order

Purchase order is the formal and final confirmation of the requirements that is sent to the vendor to supply material or services - You can click the procurement cycle to read more ....

As for the following you can also visit SAP help link here to understand more indepth from SAP themselves about MM Topics

4. Transfer Order

5. What is Sub Contracting Vendor

6. ESPE Navigation

7. Procure to Pay

8. Well watch the video continuously to learn more