USA

Hi,
Prepare for the SAT and TOEFL and apply for Bachelor's degree courses. Since you have already completed your polytechnic course a BS degree will be beneficial. Please visit university websites and check the programs they offer, see what interests you and check the entry requirements. Prepare accordingly.
I hope it helped.

Hi Rohan,
Please check some of the very popular universities such as Carnegie Mellon University, MIT, California Institute of Technology, Georgia Tech, University of California- Berkeley, McGill University, University of British Columbia, University of Waterloo to name a few, please visit their websites and check the program curriculum, you will find these as a specialization or major subject depending whether you are looking for Bachelors or Masters.

Below mentioned is the list of universities for mechanical engineering in Germany:
https://www.daad.de/deutschland/studienangebote/international-programs/en/?p=l&q=mechanical°ree[]=2&fos=0&fee[]=0&sortBy=1&page=1&display=list es.html

Yes, it can be done provided you have centers for examination in India.

You can stay for 24 months. You can check US immigration official website. MS international healthcare management is not a STEM subject. It is a management degree for health professionals. Subjects like: Health engineering, animal health, etc. are STEM subjects.

Hi Daksh,
The new SAT is scored out of 1600. When you have appeared for SAT exam?

It doesn't happen like that. First, you have to find a company who is offering you a job there. Now it depends on the company entry requirements, whether they ask for a fresher or a person with 1, 2 or 3 years of experience.
You have to check job listing on net and apply for it. Once you get an offer from there, then you need to clear IELTS paper in GT module. Thereafter, you will get a visa.

There is no government university, they have public/state and private. You can follow Times Higher Education or QS world ranking for a list of the best universities in these countries.
In USA, Purdue University, Texas A&M University, Ohio State University, Georgia Institute of Technology are few of the top public universities. University of Melbourne, University of Sydney, Monash, etc. are public universities in Australia.

Hi Rupali,
You need to keep checking university websites for Ph.D admission calls. You must first start communicating with the department supervisor or admission advisors, have a research topic on your mind and share the same with them. Additionally, you must follow the traditional admission process system such as online application form, letters of recommendation, statement of purpose, TOEFL or IELTS scores, GMAT or GRE scores, financial evidences, etc. You can check UCLA, Cornell, Michigan State, etc.