SAT

Hi Tushar,
Registration is open all throughout the year. Please check:collegeboard.org
Please specify where you want to apply for better help.

Hi Vivek,
Your scores are not the only factor which will be evaluated by Ivy Leagues. They require all-rounder and not book worms. They look for students who will contribute to the university and the school. More than 95% is not mandatory at all, but if you do its good for you. An highly academic student that is a student with more than 95% may also be rejected if the university finds the student profile not so fit for the university. Go through these links, understand the kind of profiles they take in:
https://college.harvard.edu/admissions/application-process/what-we-look
http://www.admissions.upenn.edu/apply/what-penn-looks-for

Yes, a very good SAT score does help big time.

Hi Vartika,
Please check collegeboard.org for the proper syllabus. Every topic is important, its not like the board exams you give in India. Its aptitude test and will test your aptitude in Verbal and Maths.

You will need the university admission offer letter to apply for the study visa. If the university you are applying to requires the SAT you must give the SAT. Check the admission requirements before applying.

Hi Varika,
PSAT is the preliminary SAT, more or less like a preparation. PSAT is generally taken by 10th students or test takers before taking the main SAT. You cannot really compare PSAT and SAT as one is the preliminary stage and the other is the final. PSAT is not mandatory to appear for SAT. You can take it to improve your final preparation.

Yes, it is important to have subjects like maths because most of the UK universities look for that subject but if you are planning not to pursue computer science engineering or MS then it won't be an issue.

Hi Harish,
SAT is an aptitude test for admission into Bachelor's degree programs in US mainly. It includes topics you have studied in your high school and will mainly test reading and maths skills. IELTS is the test for English language proficiency. Check collegeboard.org for SAT details, you have to create your account here and select the test dates, etc. It is simple and instructions are available. For IELTS check IELTS.org and create your account there.

For Undergraduate scholarships in US universities, the best program in India is The Next Genius Scholarship Program.

Hi Saurav,
The popular ones are:
The Princeton Review - Manya Abroad
Jambore
Manhattan
Khan Academy
and
Kaplan