The procedure for ordering records from the National Military Records Center in St. Louis:
1. Secure a Standard Form 180 (you can order from the center or download from the website).
2. Fill it in as completely as you can and submit it.
3. In a month or so you'll receive an NA Form 13041 (or one its revisions) and an NA Form 13075. The 13041 informs that the records you seek are unavailable (usually blaming the '73 fire - this form is purely advisory, you can throw it away if you wish); the 13075 is an expanded version of the SF 180. Fill this in and submit it.
4. If you complete the NA 13075 to the satisfaction of "the powers that be", you'll eventually receive an NA Form 13038, which is an unsigned, uncertified "Certification of Military Service" which will list your subject's:
a. name and service number
b. component (Regular Army, National Guard, etc.)
c. date of enlistment or induction (if a career soldier, the date of most recent enlistment)
d. date of discharge or separation
e. last rank or rating
f. dates of active service
The whole process is an exercise in futility even if you know what you're doing (which most people don't). If you have even the most minimal information required to complete the form, you've got more than you'll eventually receive. I sincerely recommend that - unless you're a masochist, or just one of those individuals who love to always have something to gripe about - you skip the whole thing altogether.