SAT

Hello Tushar,
Below mentioned are the websites for SAT preparation:
1. http://sat.collegeboard.org: It is the official SAT website, which includes practice tests and a sample question a day.
2. Answer explanations to the questions from their main practice guide are at: http://www.collegeboard.com/html
3. http://www.gale.cengage.com: It Includes help for many different standardized tests, but requires a library's license to create an account.
4. http://www.studyisland.com: It is somewhat similar to Gale, but requires your school to purchase a license.
5. http://www.sathabit.com: A provider of quick practice tests to let you see how you would do if you took the test today.
All the best.

Hello Samir,
Once you have all of the concepts down, doing well on the SAT or any other standardized test is mostly a matter of targeted practice. What sections do you struggle with most? Which types of questions (probability, mystery function, long dual-passage reading, etc.) do you have the most trouble with? Once you've identified your problem spots, focus on improving those areas while doing full-length practice exams from time to time, just to build up test endurance while gauging your overall SAT preparation progress.
As of now, many companies have assembled huge databases of reasonably good practice questions that have been tagged with a detailed breakdown of problem type and difficulty, as well as clear and comprehensive explanations. Some of these are available only in book form, but I see no reason that they couldn't be automated for practice in a web app or software package.
As to free apps, there a couple of sites that are focused more on SAT content review than practice, but they may be more along the lines of what you want:
Khan Academy has a few reasonably good modules up and is partnering with the college board to create a comprehensive set of modules as the redesigned SAT rolls out in 2016.
Sparknotes has some reasonably good material organized into different modules with post-test review questions (though many of the interactive parts are currently under maintenance).
All the best.

Hi Samarth,
Please see the application requirements page of Harvard, read the FAQs and other details carefully for the information you are looking for
https://college.harvard.edu/admissions/application-requirements
To apply to Harvard and other universities/colleges in USA, you must use the common application portal, here is the link
http://www.commonapp.org/
To take SAT and TOEFL, please register yourself on the respective official websites, select the test date and pay the fees online. Please visit https://www.collegeboard.org/ and http://www.ets.org/toefl
Regarding the two SAT subject tests, you must check the program specific admission requirements page. Generally a mathematics test is required, choose the other subject basis what you plan to study and to demonstrate your skills. Advice you to first go through the university website if you are seriously planing to apply. Good Luck.