Hi

To take admission into IIITs, you have to take entrance examinations like - JEE Mains, even few State PET examinations dependending on the IIIT. Based on your rank and merit, you will be allotted courses in IIITs. You can take admission into IIITs through JoSAA and CSAB Counselling Procedures. 

Best of Luck. 

Hope this helps.

Cheers!