The US Navy ... please explain what its like to me?

okay i am about to be a senior in high school this september. i am considering going to the navy for 2 reasons. i want to go to a good college and graduate debt free and also i want to become a detective.. or at least higher than a police officer. i figured if i went to college for 4 years and have 4 years of military expierience so i have a better shot at a good job. i just wanted to know how hard is it to get the NROTC scholarship or does everyone get it? i also would like to know what kind of jobs are in the navy .. mainly jobs that have to do with law. id also like to know if the navy sends you money while your in college (becuase a recruiter told me that you go to college first and they send you monthly checks and then after you graduate you go to the navy) i also heard from a friend that you graduate with a $20,000 check - is that true? how intense is being in the navy? please answer my questions .. i dont want to get myself into something before knowing everything.