Traditionally , the future son-in-law would ask the brides parents for permission to marry their daughter but not-a-days it is usually the bling bling of the engagement ring or a post on facebook that will give away the couples intention to marry.
Traditionally the brides parents would be told the happy news first followed by the grooms parents. The wedding announcement would then be told to family and friends. Newspaper and telegram announcements are now rare especially since the introduction of social media.
Some couples still may choose to have an engagement party which traditionally is the official time the announcement would be made.
If one or both parties decide to break off the engagement then it may be possible that one or both of the partners may ask for the engagement ring back. Etiquette demands that the ring should be returned, especially incase it was a family heirloom. All money and gifts should also be returned to family and freinds.