USA

Hi Nilay, what you should study should be known to you, if you still haven't decided then I think you are not prepared to go abroad yet. If you are confused with the subjects then find out your aptitude, likes and dislikes, favourite subjects, most hated subjects etc. There are many courses offered by universities in US, you can browse through university websites and find relevant majors etc and also you can choose your major later.
To get a scholarship you have to do well in your academics, SAT etc and must also have extracurricular activities. Target a SAT score of 1400 and above. Start researching on university admission requirements and prepare accordingly.