You can make an unarmed melee basic attack without the usual –2 penalty, and you choose whether to use Strength or Dexterity to modify the attack and damage rolls. If you hit, you deal 1d8 damage per level you possess, plus any modifier from Strength or Dexterity (which is doubled at champion tier and tripled at epic tier). If you miss, you deal damage equal to your level.
Champion Feat: You can make an unarmed melee basic attack as above as a quick action in addition to your other actions on your turn. However, if you take another action during that turn to use an attack power or basic attack, this attack deals only half damage. (Any miss damage is not halved, however.)