This is the very first part of the Air Force Academy admissions (the Naval Academy does something similar), and is pretty straightforward. Based on this, it's decided whether you may continue with the process, or are better off looking at some other college. It's divided into a few different sections (whose names I made up myself):
ID: This is mainly name, age, address, sort of thing. Pretty simple, although one question about race threw me off. As a half Caucasian, half Hispanic mutt, I thought it should be easy, but it wouldn't let me mark both Hispanic and Caucasian. I look more Caucasian, don't have a Spanish accent, so that will have to do. Make sure you know you're ZIP code (or in my case, my Postal Code), and how to properly write an address (which pretty much no one ever has to do anymore, what with that newfangled invention, the Intertubes...).
Grades: this includes SAT/ACT, class rank and GPA. I worked out my GPA myself because my school doesn't grade in those terms (strictly in percentages here). Either way, later on your school has to send your official grades and your GPA is recalculated.
Hint to those who have to fill this out. Wait until you have you have all your information ready, yeah, you can update it later, but to update this section you actually have to call the academy, you can't just sign in and change stuff. I sent it in before I had my SAT scores, tried to call a couple of times, got no response and sent an e-mail begging forgiveness (because it specifically said call) and asking for help, along with a few unrelated questions about sources of nominations. A few days later, my scores showed up on my profile, but I didn't get an answer to my e-mail, so I think it's probably a result of having sent the Official Score Report through College Board. Moral of the story: have your grades ready.
Miscellaneous: questions about extracurricular activities (scouts, church groups, etc), whether you've applied before, if you're in college, military, or high school, if your eyesight is correctable to 20/20, whether you've held a job, and a whole slew of other stuff. I think they're all yes/no questions.
Once you send this in, you're an applicant. If the powers that be consider you adequate, you're a competitive applicant. Later on, after they get some more information, they decide if you get to be a candidate. You can get to be a candidate without a nomination, but you need one to have a chance of being accepted. You can get a nomination and still not be considered competitive. Right now, I'm a competitive applicant.