Brazen Boarding 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

Brazen Boarding deals 4 damage to target creature or planeswalker. If excess damage is dealt this way, conjure a card with mana value equal to that excess damage from Brazen Boarding's spellbook onto the battlefield. If that excess damage is 4 or greater, instead conjure a card named Admiral Beckett Brass onto the battlefield.