Why does the navy and air force have special forces? What do I have to do to get in?

I want to join either the seals or the air force special ops after being a pilot for a few years. How do I transition? Why does the air force and navy have these special operations? Why not leave it to the Army and the Marines? I read that air force spcial ops specialize in taking over airports and seals specialize in beach stuff but don't too far? I don't know how reliable this source is but I was wondering why they have these programs? Do navy carriers cary armed personnel aboard? I'm only 15 so I have a lot of questions that need a lot of answers! LOL I'm going to start doing Seal workouts tomorrow and am reading some books by Couch. What kind of prerequisites do I need? Like officer training in the air force (BOT)? Or the naval academy? Or should I just get a college degree and then just enlist in the navy? But if I would be an aviator in either how would I transition to special ops?