So, realistically, that's really all you need to know to understand how it'll play out in-game. For those looking for more detail, here's what's happening behind the scenes:
The boss dies.
Each player has a chance to win loot, independent of the other players.
For each player who wins loot, the game randomly assigns them a spec-appropriate item from that boss's loot table. This subset contains only items that the game (meaning the designers in this case) thinks are appropriate for your class and current spec.
Notice that you aren't rolling Need or Greed. You don't have an option to Pass. The game just says "Take this."
You can't trade this item, or that would defeat the purpose of removing the social pressure on groups of strangers. If you don't want the item, you are free to vendor, delete, or disenchant it.