You can make a Whirlwind attack as the first action of your turn when you are engaged by two or more enemies.
You take a –4 penalty to your AC and PD until the start of your next turn. Then roll a separate melee attack against each enemy you are engaged with. You deal no miss damage with these attacks.
You now deal normal miss damage with missed Whirlwind attacks.
The penalty to your AC and PD is reduced to –2. In addition, disengage checks you make the same turn as using Whirlwind automatically succeed.
You can use Whirlwind anytime during your turn, not just as the first action.