Unfortunately you cant apply for security clearance on your own. Your employer must file and you can only get the clearance for information that you need to do your job. Your employer will complete a Standard Form 86. You will be fingerprinted and will have to sign a form giving them permission to investigate your background. Make sure you are completely honest on the form since its illegal to withhold information. Then you just wait for the background checks to come back and the administrator officer of the agency that requested your clearance will decide if its granted or not. Good luck!