In order to apply for CAT Entrance Exam you should be Graduate in any of the field, It depends on your capability & Interest, If you wish to get into Corporate world then you can go for Management programme to score well in CAT Entrance Exam.

CAT is the national level management entrance exam conducted by Indian Institute of Management for admission to 20 IIMs and more than 100 B-schools across India.  The final admission is based on  Group Discussion (GD) or Writing Ability Test (WAT) or both and Personal Interview (PI) rounds along with CAT score & your past academic records. You can check the further information about the exam with the given below link.

https://bschool.careers360.com/exams/cat

If you are preparing SSC CGL, It will also help you some where for CAT Entrance Exam.

Good Luck!