If you are talking about the builder event, and you posted in that category, the mentioned „coins“ are the snowman coins that you get in exchange for the divine snow. I‘m very sure that you don’t have 2,5 million of them 😉
To buy green rings or amethysts with those snowman coins, you go to the shop, choose „new“ on the app, Home and New stuff on PC.
As for checking how many you have, the rings are where gamemaster said. The amethysts are in the material tab of your inventory. As are the snowman coins.