You will need to register with Tamil Nadu Selection Committee for management quota seats. Next, participate in the counseling. If you have a good score within your diocese, you will be shortlisted and get an admission letter. After that, you will need to visit CMC Vellore to complete the admission process. 

To get the eligibility certificate from Dr. MGR University, you can visit the campus with all required documents and make the payment at the bank counter there. You can also apply for the EC online. EC is not needed for counseling. But you will need it to complete your admission.