So basically machan a fresh graduate even with a masters degree won't take you to higher ranks unless you got some contacts in the organization. Basically you will start with the executive post, probably as a management trainee. And with your masters and work, you will probably end up in Assistant manager level in 2-4 years. This will vary

since its Srilanka. It can be up to 5-8 years also
Basically in manufacturing management you will learn Lean, Industrial engineering principals, supply chain management principals. some part of HR. More in to how manufacturing process can be optimized. But if you are willing to go for a master I better recommend a degree with Data Analytics since it's kind of hot topic these days and there are plenty of vacancies .