RN vs. BSN--
Once upon a time, in the U.S., the standard nursing schooling was a 3-year "diploma" program (in the days of starched white uniforms and distinctive nursing school headgear). Very few of that model exist today, tho there is one in this local area. The great advantage of these programs was that nearly a full year, full time, was spent in clinicals--beyond one what can expect today in a 2-year program. Graduates of these programs could "hit the ground running" in nearly any hospital unit.
A "2-year" ADN (Associate Degree, Nursing) program will qualify one to sit for the NCLEX (pronounced EN-clex). (National Council Licensing Examination.) Only by passing this test may one qualify to apply to one's state BON (board of nursing) for a license as an RN. Until you get that license, you are not an RN; you may be styled temporarily as a GN (graduate nurse), for work situations in specific hospitals or other employers.
These programs are typically administered by junior colleges/community colleges; and are called 2-year programs because after having completed whatever the prerequisites are (which vary), the nursing school program typically requires 2 calendar years to complete, if all goes well. There are also some for-profit private entities conducting such programs, from what I hear.
BSN programs (Bachelor of Science in Nursing), commonly called 4-year programs, are typically offered by full-fledged 4-year colleges and universities. IMHO--for which I'll get flamed, no doubt--this amounts to a 4-year college degree, with a major in nursing. But, I have never heard it referred to this way. Such a program equally qualifies one to take the NCLEX, and upon passing, apply to one's BON for a license as an RN.
A "quick-and-dirty" overview could be stated as something like this: A 2-year program can get you sufficient basic nursing knowledge to be able to function as a brand-new RN, with little or no actual experience. So can a 4-year BSN program, but you will have a college bachelor's degree. (Do note that I said, can get you sufficient . . knowledge . . . ) And I expect many will disagree with this summation.
Some students feel that a 2-year ADN takes the "same" amount of time as a 4-year BSN, when one factors in the time required for prerequisites. And this may well be so.
Another factor to consider is cost. In my area, one of the highest in the state for community college tuition, one credit hour will cost you about $140. A reasonably nearby branch of the state university, with a "low-cost" reputation, charges $400 and some, for one credit hour. The diploma program mentioned above charges something like $475 per credit hour.
And there may be other fees tacked on to these tuition amounts, in all cases.
Practicality--it depends on what you want to do, or do eventually; and to some extent, where you want to do it. There is a distinct trend in the land today, to require more formal education than previously, to do much the same professional work.
Thus, some hospitals--just for one example--may require that brand-newly-hired RNs have earned a BSN, for various reasons. In such cases, a 2-year ADN won't work.
I hope that this lengthy attempt at an explanation will answer most of your questions, and give you enough to chew on.