Saikumar,
Not sure what you mean by "joined now in SAP MM". Do you have a job where you do SAP MM? Are you planning to take coursework through a certified training provider?
In general, I recommend you buy an overview book on SAP and on SAP MM. Also, check out one of the many youtube overviews of SAP and/or SAP MM. This should help you get your bearings a bit.
You might want to check out
Hope this helps!
Best regards,
--Tom