Hello Tilak :)

Firstly, if you want to enter into a university in the US, you need to be fully prepared so that there is nothing we have left unattended.

I am assuming that you must have checked out at least a few colleges depending on the course you want to pursue. If you haven't, I recommend you do that immediately so that you don't miss the application submission dates. Also, prepare a list of the colleges you would like to apply to. Don't pin all your hopes on one college and apply only to that one.

Once you have a list, check out their websites for the application forms and procedures. Some universities have a downloadable form, whereas for some, you need to request them personally (eg: via email).

Now, for the documents:
1. School reports - You need to have your 12th standard marksheet and reports signed by the school authorities. The reports should contain your performance in your exams (held throughout the year) as well as your achievements in other fields.

2. Letter of Recommendation - A letter of recommendation basically states your performance in academics and extra curricular activities along with your behavior in and around school. It should be written by an authoritative figure who knows you academically and as an individual (eg: class teacher). It is better to attach at least 2 such letters to increase your chances of acceptance.

3. Statement of Purpose - This one is all about you, something that you have to write. You should state your reason for choosing their college, education, experiences, interests and goals. Some universities have a specific format, which if not followed, leads to rejection of application. So, do get in touch with the university regarding this.

Let's have a look at the tests involved:
1. TOEFL - mandatory for international students; tests English proficiency
2. SAT I - required by all universities; also known as SAT; contains reading, writing and mathematics
3. SAT II - required by some universities; also known as SAT Subject Tests; contains various subjects, choose based on university requirement
4. ACT - required by some universities

Having crossed all these hurdles, the last step may or may not include an interview. It could be telephonic or through a video call. It is usually informal and is done to assess the individual personally.

Hope this helps!
All the best to you for your future.