The Borg Queen 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

Artifact creatures you control get +2/+2. Whenever The Borg Queen enters or attacks, target opponent exiles cards from the top of their library until they exile a creature card. Assimilate that card. They put the rest on the bottom in a random order. (To assimilate a card, put it onto the battlefield under your control with a +1/+1 counter. It's a Borg artifact creature and loses all other creature types.)