Get a High School Diploma or a GED and get a good score on the ASVAB test. Call a recruiter to know more. If you want to be an officer you should ask about ROTC. To become an officer you can go to a Commissioning School like West Point or Norwich University, many colleges have ROTC programs, there are also OCS which if you already have a degree can be another path and direct commissions but in recent history they have only been given to accomplished soldiers with years of enlisted time.
If you are interested call a recruiter because they will have the most up to date information of the options and career available to you.