Every college has different form available on their website.

In that your 12th score and nata score will be added and a merit list will be formed on the basis of 50-50% .

Then according to that list admission will be given

You can go to college and approach them or try online checking for colleges of your desire and their criteria like cutoff ranks and decide on fees and other criteria. Because all colleges have their own procedures of admissions.

Visit this website for more information: www.coa.gov.in