By the time of the question posted, I think the time is gone already. You should have taken TANCET 2020 which happened on Mar 1, 2020. The results were out by March mid itself. Based on the score and the rank assigned, the rank list will be released by Anna University.
The call for counseling follows the released rank list and you will be invited to GCT, Coimbatore to choosw the colleges that you wish to. If the seats are available for the college you wanted, you can choose the college and other process will follow at the chosen college itself.