Jet Collector 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

At the beginning of your second main phase, if there are four or more cards in your graveyard, conjure a card named Mox Jet into your hand. This ability triggers only once. : Return target creature card with mana value X from your graveyard to the battlefield with a finality counter on it. Activate only as a sorcery.