Answer:
An engagement is a promise of marriage and is worn on the left hand. When you marry the engagement ring is removed and the wedding band is placed on the left hand. Then, the engagement ring is put on top of the wedding band. Both are worn on the left hand. I just double checked this since I got married two weeks ago and wanted to be sure that the bands were worn correctly. The engagement ring on the outside of the wedding band is a traditional method to wear it.