The Wedding Ring is a craftable Pre-Hardmode acessory. When equipped normally, it does nothing, but if you are married with any of the "marriable" Npc's, it will grant specific buffs depending on the Npc.
|Gold bar (5)|
"Blushes Did you read all of it senpai? That words are only fragment of my love. If you accept I want to share my heart with you but I want it to be how I dreamed. In my dreams I wear a bride costume as white as swans so could you find it for me?"
That indicates that you need a Wedding Set, obtained from The Bride. After you obtain the wedding set and click the letter option again, a new option will replace the "Give her letter" entitled "Give her wedding dress". If you click that option, the yandere will say:
"Blushes Senpai that's as white as your heart. Looking at it only makes me love you even more. Now could you bring me a wedding ring and finally let us become a perfect couple?"
Now, that indicates that you need a Wedding Ring. After you craft the ring, bring it to the Yandere, and a option will appear, entitled "Give her both your heart and ring." After that, the Yandere will say:
And a heart will fly upwards, exploding into confetti. If you equip the Wedding Ring after that, it will give you the Heart of a Killer buff.
"That looks as elegant as you. Thank you and I accept you as my couple. Please afetr you finish your job let's settle into a place that consists of only me and you."