Fill your choices, wait for results of the 1st round, go to nearest nit/iit depending on the seat u r alloted in 1st round whether its nit/iit. Do necessary documemt verification and all. Chosse either float if u want to participate in further rounds, freeze if u want to lock ur choices amd slide if u want only the branch upgradation.
If u choose float, wait for next or further rounds results. U have to go to the alloted college if you want to freeze ur choice.