Note: The following is from my memory and is based on last year’s process. Verify all of this for yourself by calling the National Merit office or another reliable source. My information could be wrong or outdated!!
You should get notified if you are a semi-finalist around mid-September. There is then an application to be sent in to see if you qualify for finalist. The application includes an essay and a summary of awards/extra curriculars. You also need to make sure you send your SAT score to the National Merit corp. It is not automatic; you have to ask for the score to be sent. Last year the application was all done online, so I’m not sure what a previous poster is referring to when he/she says “mail in” things. Your high school counselor will need to do part of the application, too. I think the counselor includes your transcript as part of the application. Make sure you, and the counselor, meet the deadline you are given!! I remember it seemed like a rather short time in which my child had to submit the application for finalist.
Definitely consider applying to any FL schools you are interested in, and look up the Florida Incentive Scholarship. If that scholarship exists next year (it might get voted down by the state) you could get offered a free ride to several of the state schools if you make it to National Merit Scholar (not all of the schools participate in National Merit).
If you plan to apply to UCF, you might want to wait until your semi-finalist status is announced. If they operate the same way they did last year, they will contact you and will waive the application fee and the essay requirement for semi-finalists. UCF will invite you to a couple of events for semi-finalists/finalists. (again, if it is the same way they did last year).
The process is a bit confusing. You will eventually have to name a first-choice college on the National Merit site. Make sure to do so by the deadline. Don’t be afraid to call the National Merit Corp office to ask any questions. Don’t blindly trust what people post on this site (although most times the info on here is pretty accurate) including my post!! Verify, verify, verify!!
Good luck!!