Hello Ravi Shankar

Through JOSAA, you can take admission only in IITs, NITs, CFITs. You can get an IIT only if you qualify Advance and not on the basis of Main.

For other private and government college, you need to register separately for each. You will have a cutoff that you need to cross for getting admission in a college for a particular branch. All colleges and all their branched have different cutoffs.

Hope it helps you.