Ring of Kalonia is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Equipped creature has trample. (It can deal excess combat damage to the player or planeswalker it's attacking.) At the beginning of your upkeep, put a +1/+1 counter on equipped creature if it's green. Equip (: Attach to target creature you control. Equip only as a sorcery.)