UK

Hi Reyansh, UCAS Tariff is a point system used by the universities to set their requirements. It is something you don't have to worry about. You can check the internet and the UCAS website to learn about it if you wish. Now, UCAS is the common application system to apply to the universities in UK mainly for undergraduates and some post graduate programs. UCAS is not merely some requirement but the portal through which you apply to an university in UK. Ever university here in UK is grouped in UCAS accordingly and you have to apply by the given deadlines and upload required documents. The basic eligibility to study CS if you are talking about Bachelor's degree, you have to complete your 12th and take the IELTS. Majority of the universities here require more than 70% in 12th to be considered for admission.

Hi Midhun,
Both these countries have part time work schemes for its international students. But, off late a number of rules and regulations have changed in both. If you have been viewing international news and have been updating yourself with global affairs you will know that UK 's work permit options for international graduates that is after you complete your studies have gone very rigid and strict. If you are planning to stay and work in UK after studies its not going to be easy. News is also there that India does not recognize one year MS degrees from UK anymore. I will advice current aspirants to carefully judge all situations and apply. Contact the universities you are interested in and enquire about the career assistance, work permits etc. Similarly in USA, you must take the GRE to apply to universities. As part of STEM you will be eligible to work for a year or so after studies. Its competitive and depends on your class performance. Before finalizing assess your budget as well.