there is three levels of nursing: LVN, RN, NP. becoming an NP is a lot harder than becoming an RN, but not as hard as becoming an MD.
for an MD, there is 4 years of college, then 4 years of medical school. then you take the exam to become an MD. then there is a minimum of 1 year of internship, but more often 4-5 years of residency specializing in some field. then there is taking the board exams for your specialty. then often a fellowship.