Being a finalist means that you have met the preliminary qualifications and are qualified to interview for a scholarship offer.
Initially, before you go to your interview, you'll take a PT test to take with you to your interview. Then at the interview, The officer will ask you a couple of pretty standardized interview questions (What can you do for the Army, What do you want to do in the army, etc.) It's really not a hard thing to do, and like what some other of the posts have said regarding the interview, just be yourself, remember your formalities, and you shouldn't have a problem.
Here's a tip that I learned in my process too: It's pretty common sense when you think about it, but interview at the school you're planning on getting the scholarship at. In your letter, it gives you a couple of schools in your proximity that you can interview at, but it's best to go to the school you've applied for. (Being accepted before hand is key in the process, is what the PMS told me)
Your interview will then be sent to a national review board that takes in all applications and meets about once a month to review them and make a decision as to whether or not you get an offer. For me, it was about 3 weeks after the board met that I received the offer in the mail, and also you can follow it with the online application tracker.
That's pretty much the jist of it, Good luck with it!!