Hello,
You need to fill the application form of the respective state and then wait for rank list after that awindow for setting up preferance will open.
After setting of preferances the students with high merit will be  alloted colleges according to their prefernces of the colleges.

You can wait for subsequent rounds if you arenot alloted a college or want to hange the college and get into a better one.

You can use careers360 college predictor to know the colleges you can get at your NEET score:- https://medicine.careers360.com/neet-college-predictor?icn=QnA&ici=qna_answer