Inys Haen 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

When you planeswalk to Inys Haen and at the beginning of your upkeep, mill three cards. When you planeswalk away from Inys Haen, each player returns all land cards from their graveyard to the battlefield tapped. Whenever chaos ensues, return target nonland card from your graveyard to your hand.