Hello there. Let's talk about all these institutes separately.

Starting with IIT, IIT is the biggest educational brand in India. It is being considered that if someone has got admission in IIT, then he has got a sorted carrier. To get admission in IIT, you need to qualify JEE Advance which is considered as the toughest exam in India. Also IIT is a autonomous body i.e. they take their decision on their own and doesn't depend on government.

Next comes NIT. NIT are being considered as the second best educational hub in India. Like IIT, NIT are also autonomous bodies and they are associated with the IIT. To get admission in NIT, you need to qualify JEE mains with a good rank then only you can get admission in NIT.

IIIT are the institutes which comes after NIT. These are also considered as the best college in the terms of jobs and placements. The environment here is somewhat same as that of IIT AND NIT. 

GFTI are the institutes which are being funded by the government i.e. they are dependent on government. Most of the times GFTI are being preferred only because of fees. Since they are government funded so they are not having high fees. The process of getting admission in GFTI is also same as NIT and IIIT i.e. based on JEE mains ranking.