You can opt for a certification course of SAP MM in a particular module. As per your interest in a specific profile like:
1)SAP MM if you are interested in Purchasing, Material Handling, stores and so on
2) SAP SD - for sales and marketing
3) SAP FICO - for finance, audit and so on.
Similarly, they have plenty of other modules as well. And, if you are a working professional then I would suggest you opt for an SAP module relevant to your job profile as per your domain experience and if you are fresher then you can go with the online course provided by a well-known institute like Intellipaat, Unacademy, etc.
Check out this course:
Here, you will be trained by industry experts with a lot of hands-on experience. Along with that, you'll get the following services like 24*7 technical support, lifetime accessibility, of course, assessments after every lecture and a lot more.
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: