What are the best sites from which to learn SAP MM?
You can start learning SAP MM from a recognized institution that offers you SAP MM course at a much lesser price. One such course provided by Intellipaat is as follows:
https://intellipaat.com/sap-mm-pp-certification-training-course/
Here, a lot of blogs, tutorials are there that explain the concepts and understanding of how MM works.
If you want to learn SAP MM from scratch, then here's the right video for you:
If you are more into reading, then do check out this material provided by Intellipaat:
https://intellipaat.com/blog/tutorial/s4-hana-logistics-tutorial/