At 0 HP your character falls unconscious and starts making death saving throws — a raw d20 on each of your turns. 10+ succeeds; three successes stabilize you, three failures and the hero dies. Allies can stabilize you (DC 10 Medicine) or bring you back with healing.
Death is honored, not undone. A fallen hero gets an epitaph and lives on in the campaign journal and chronicle memorial. You create a new hero and the story continues — the world remembers the one you lost.