How to play Ring of Valkas?
You can only equip the Ring of Valkas as a sorcery (so, only during one of your main phases) but once it is equipped, the Ring stays on the equipped creature until it is moved or the creature dies. So, you put it on your creature this turn and it starts getting counters on it during your next upkeep, assuming it's still alive.

Edit: Looks like I missed part of the question. Any +1/+1 counters remain on the creature, even if you move the Ring to a different creature, or the ring is destroyed.