Find the USNA website...Then the NROTC one.  Those will have the official requirements. 

For USNA, you'll need grades/test scores, sports, clubs/activities, leadership (much like any service academy) 

You need to apply to USNA, plus get your DoDMERB physical, and a nomination (check your Congressman's, Senator's, and the Vice President's offices/website for thier applications)

Like I said, the Naval Academy's website should have specific steps to take.  The Navy ROTC site will also.  CHECK FOR THE MARINE OPTION on both.