Hi Nityam!!

It is basically level by level procedure. You have to qualify a couple of exams like Jee Main and Jee Advance with good rank for having admission in an IIT and then you get a seat through counselling.

You just have to qualify Jee Main for having admission in NIT and IIIT. Candidates are selected on the basis of merit and then a counselling session happen for distribution of branches and colleges.

For more information like eligiblity, pattern, etc. follow the link:

Jee Advance

Jee Main

Hope it helps!!