When you cast energy vortex, you choose one of five energy types: acid, cold, fire, electricity, or sonic.
A blast of that energy type bursts in all directions from you, dealing 1d8 points of damage +1 point per caster level (maximum +20) to nearby creatures other than you.
If you are willing to take the damage yourself, you deal twice as much damage.
You don't get a Reflex save, but spell resistance applies, as do any resistances and immunities you have to the energy type.