Quench 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

Counter target spell unless its controller pays .

How it works : Quench

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Quench.

Quenchable Fire

Quenchable Fire deals 3 damage to target player or planeswalker. It deals an additional 3 damage to that player or planeswalker at the beginning of your next upkeep step unless that player or that planeswalker's controller pays {U} before that step.