If you already have a BS degree how would you go about getting a nursing degree?
You would need to find a nursing program that you like and that fits your needs first. I recommend this site:
Then, you need to speak with an admissions advisor at the university/college/trade school to get accepted. You will then need to meet with an ARTICULATION COORDINATOR, as you are likely not going to need to attend the full two years required to get an R.N. license. Chances are you have already met all if not most of the general education requirements, and you may have already taken some of the science classes required. They will look at your official transcripts, and then asses what credit will transfer and what won't. Don't be surprised if a LOT of your credit won't count, depending on what BS degree you have. An example would be a BS in business administration. I'd bet that the overwhelming majority of classes in that degree would not be transferable towards a nursing degree. It's really up to the school and their requirements.
You have to remember that nursing is extremely specialized, and there are many classes in the degree program that are specifically "nursing" classes that you wouldn't ever have taken. Even if a Pre-Med undergrad with a BS degree in Biology went to get an RN, he would still be lacking probably a year's worth of specialized nursing clases. But you'll never know until you sit down with the articulation coordinator.