UK

Hi
For USA, you need to prepare for SAT/ ACT and TOEFL/IELTS. You can apply through common app and will also need letter of recommendations and SOP. Your high school transcripts are also required to be uploaded in a standard format.
For UK, you can apply through UCAS.
Since British students undergo thirteen years of pre-university education as compared to twelve years in India. Outstanding marks from one of the two Central Boards (CBSE or ICSE) or their equivalent, or the first year of an Indian degree programme are therefore usually required for direct entry into an undergraduate programme in UK.
For those who do not, as yet, have these qualifications, there is a range of access or foundation courses available. Foundation courses range from four months to a year.
Applicants must satisfy both general and course requirements for admissions :
General Requirements
A specified number of subject passes at both GCE "A" Levels and GCSE at grade C minimum is required for admissions in UK educational system. An equivalent Indian qualification such as a good score in the CBSE and ICSE etc with 80%.
You may also require to take TOEFL/IELTS for english proficiency.