Greetings!

The first step you should take is to decide which colleges or universities you want to apply for. After you have decided where you will be applying, go through their website and read about their admission process thoroughly. Some colleges might conduct an entrance exam or some might simply take you based on your merit (Class 12 marks). I don't think there is a centralized system for admissions to B.Sc. Nursing, so you might have to apply for each college/university individually. 

To know the best colleges offering B.Sc. Nursing course, refer to this link - https://www.careers360.com/news/4433-Course-review-Nursing

Hope this helps. All the best!