There are different degrees that make up the same designation of R.N. A Diploma R.N. which studied and trained in a hospital-based environment working as staff in the hospital for hands-on experience in the off shifts of class time. This takes about 3 years. The Associate Degree nurse (ADRN) has a 2-year college degree. The Bachelors in Science in Nursing (BSRN) has a 4-year college degree. These degrees mean college courses first, then hands-on experience -- clinical time.
Nurse Practitioner (N.P.) or Advanced Nurse Practitioner: R.N. with a Masters degree who practices under the license of a physician to do almost everything a physician does, such as diagnose, write prescriptions, give orders for tests and referrals, etc. Nurse Midwives fall under this category as well.
P.A. or Physician's Assistant is usually a non-nursing person who has 2 additional years of college on top of their 4-year Bachelor's degree and has similar capabilities as the Nurse Practioner.
MSN (masters degree in nursing) or PhD in nursing typically are educators in nursing schools