ACT

Both of these are the entrance tests for doing engineering related courses abroad. Please upvote if you found this answer useful.

Hi Swapnil,
I believe you are enquiring about scholarships. If yes, then please know that there is a difference between fellowship and scholarship. Be careful with the terminologies when you are applying abroad. Scholarships are on merit-basis, a high SAT or ACT score will increase your chances, however, not a guarantee. You must be a brilliant student overall.

Hello Shambhavi,
You can take either one of these. You need to know the difference between both and decide which seems easier for you. Here are two articles which can help you compare and decide:
https://studyabroad.shiksha.com/everything-you-need-to-know-about-the-sat-articlepage-286
https://studyabroad.shiksha.com/act-american-college-testing-for-admission-to-undergraduate-colleges-in-us-articlepage-97

Hi,
Start preparing your application process including taking these tests a year before the admission sessions. You can schedule the tests accordingly. Visit university websites for upcoming deadlines and prepare.

Hi,
There is no set eligibility but to take SAT or ACT, you must be a high school student as these tests are given to study Bachelor degree. For TOEFL, there is no such requirement.

Hi,
You have to apply to the universities through common app or individually. Your SAT/ACT scores are sent directly by the respective agencies. With your application you will be required to submit your high school transcript, letter of recommendations from principal/counselor and teacher, an essay or Statement of purpose, etc.

For Ivy League colleges, you need high academic scores, SAT and TOEFL/ IELTS and a good overall profile that may include confidential curricular activities, projects, innovations and leadership skills.

Hi,
Apart from the test mentioned by you, there is AP programme in which you can choose the subjects and take credits before joining the course in USA by clearing it with good score.
The scores in ACT, SAT or TOEFL/ IELTS depends on which universities u plan to apply. Higher the score, better are the chances of scholarships. For SAT any thing above 1280 is considered good.

You can go for either one as both SAT or ACT is accepted by US universities. Both the tests are a little different and you can decide which seems better and easier for you basis the format, syllabus, etc.
You can check the below mentioned link:
https://www.princetonreview.com/college/sat-act