Okay, technically halal is anything not forbidden by the Quran (haram). So they're good if they keep away from pork and other haram foods. What they're really talking about is dhabihah, the ritual slaughter that is almost exactly the same as kosher (kashrut). In common speech people tend to just say halal.
But to your question, the throat is deeply cut with one quick slice severing every blood vessel, and the animal is allowed to bleed out.