Could you please list me the important exams other than the entrance exams a 12th standard person ( PCM CS )should be giving ? ( like KVPY , scholarship exams etc )

Since, you are a student of Class 12th student, so you are eligible for KVPY SX exam. The important topics for KVPY are the same as for JEE except the difficulty level is slightly less. The way to prepare goes as- Understand the conecpts thoroughly, prepare the JEE Mains paper thoroughly.