He takes ASVAB. Based on scores will determine what branch(es) he's eligible for. It's USAF, Navy, Marines, Army in that order. Not that the Army is the bottom of the barrel but they do cover a lot of career fields.
Every branch will give you a guaranteed MOS, AFSC or whatever, but you have to be careful in dealing with the recruiters.
Go here:
http://www.military.com/
and go to their Features page. There is a wealth of straight up, honest material on everything from prepping for the ASVAB, what to do before, during and after Basic and much, much more. If you're not that computer literate, post and I'll provide you with direct links.
I can say something good and bad about every branch of the service. And some folks are a better 'fit' for some branches than others.
Me, semi-retired (waiting for 60) USAF SMSgt, (E-8 for you other branches) and I've done Reserve, Nat'l Guard, contingency activation, Active duty. Haven't done it all, but done a lot.
It's a life-changing decision and rarely to the negative. He could do worse.
Please post on what's he's going to do.