The Graduate Record Examinations (GRE) is a standardized test conducted by the Educational Testing Service (ETS) for admissions to the graduate programs in the United States Of America. This is the test you need to take if you are aspiring to do your graduate studies (Master's or PhD) in the United States. GRE comes in two formats - computer based and paper based. The paper based test is conducted in countries with limited computer facilities. In India, the only format available is computer based.
Computer Science was discontinued since April 30, 2013.
Some universities with highly competitive programs, specifically PhD, expect students to submit subject GRE test scores. This information can be found in the web pages of the universities you want to apply to. If no information is given, then that means they do not expect students to submit GRE subject test scores. However, if you feel that taking a subject test will give you a better chance for scholarship and admissions then do email professors or graduate coordinators of the programs for more information.