You should have been informed of your eligibility at time of separation, if you are uncertain contact your CVSO (www.macvso.org)  (link to the CVSO tile/page)

https://www.va.gov/health-care/how-to-apply/

To enroll, you can:

1. complete an application for enrollment in VA health care by telephone without the need for a signed paper application. Just call 1-877-222-VETS (8387) Monday through Friday from 8 a.m. until 8 p.m. Eastern.
2. apply online at www.va.gov/healthbenefits/enroll, or
3. apply in person at your local VA medical facility