Hey there!

For applying to the colleges in USA, you will have to start by appearing for SAT or ACT. Additionally, you would also have to take English proficiency exam like TOEFL and IELTS.

After thats done, you will have to start working on your CommonApp application (it is an application form required by most of the colleges in USA).

You will then have to approach your teachers for recommendation letters (for most colleges, you shall be requiring a maximum of three recommendation letters; two from subject teachers and one from your school counsellor). Your school counsellor will be responsible for uploading your transcripts (results) from standard 9 till standard 12.

You will also have to start wroking on your CommonApp essay; an essential component of your application.

For more information regarding the CommonApp, SAT, ACT, TOEFL and IELTS, you are advised to visit the following sites:

https://www.commonapp.org/

https://collegereadiness.collegeboard.org/sat

https://www.act.org/content/act/en/products-and-services/the-act.html

https://www.ets.org/toefl

https://www.ielts.org/

Make sure you check the respective college's (in which you are planning to apply for) website and go through their admission requirements for international students.

Hope this helps. All the best!