Which course should I pursue to become the manager of some MNC? I have completed my class 12th (science).

It's good to have long term goals. You need to make sure that you graduate from a good university with the specialization of your choice, and then pursue MBA or Master's degree. Later, you need to set your goals and work hard to achieve them. UG courses like engineering, B.Com, B.Sc or LLB will help

Go after MBA from a reputed B-school. First, complete your graduation and focus on your current skills.