Hello..shubham..

After GATE exam you have to apply in IIT colleges individually and then they may call you for test or you may get direct seat on gate score basis.

This was  till 2017. From next year COAP will be introduced fully and hopefully from last year onwards there will be no need to apply individually because common admission portal is there.

So  you will need to register only in the COAP and fill your choices and then accordingly you will get seat or will be called for further rounds of test.

Hope this will help you ..

Good luck.