Your Vietnam veteran relative’s DD 214, or discharge paper, records basic service information. (Identifying details are removed in this example from the National Archives.)
Your relative’s DD 214 might not specify “on the ground” service in Vietnam. That’s not uncommon, I learned by Googling DD 214 Vietnam.
The form also is loaded with acronyms. Search for them online and consult a military acronym dictionary to help you translate the form.
AR 635-200, for example, is a regulation that allows for separation from active duty. You’ll find it on most veterans’ discharge papers.
A term like “APO SF” under Last Duty Assignment indicates Army Post Office (served through San Francisco). A numeric code might follow it. You can look up the code on this website to get a general location in Vietnam.