Types of Preference

To receive preference, a veteran must have been discharged or released from active duty in the Armed Forces under honorable conditions (i.e., with an honorable or general discharge). As defined in 5 U.S.C. 2101(2), "Armed Forces" means the Army, Navy, Air Force, Marine Corps and Coast Guard. The veteran must also be eligible under one of the preference categories below (also shown on the Standard Form (SF) 50, Notification of Personnel Action). *Military retirees at the rank of major, lieutenant commander, or higher are not eligible for preference in appointment unless they are disabled veterans. (This does not apply to Reservists who will not begin drawing military retired pay until age 60.) For non-disabled users, active duty for training by National Guard or Reserve soldiers does not qualify as "active duty" for preference. For disabled veterans, active duty includes training service in the Reserves or National Guard, per the Merit Systems Protection Board decision in Hesse
v. Department of the Army, 104 M.S.P.R.647(2007).
For purposes of this chapter and 5 U.S.C. 2108, "war" means only those armed conflicts declared by Congress as war and includes World War II, which covers the period from December 7, 1941, to April 28, 1952.
When applying for Federal jobs, eligible veterans should claim preference on their application or resume. Applicants claiming 10-point preference must complete Standard Form (SF) 15, Application for 10-Point Veteran Preference, and submit the requested documentation.
The following preference categories and points are based on 5 U.S.C. 2108 and 3309 as modified by a length of service requirement in 38 U.S.C. 5303A(d). (The letters following each category, e.g., "TP," are a shorthand reference used by OPM in competitive examinations.)

* This may require you to pursue the Schedule A Letter.
RESOURCE:
http://www.opm.gov/policy-data-oversight/veterans-services/vet-guide/