You may make a WIS Test to avoid damage from incoming blaster fire which you are aware of.
If you pass by 5 or more, you can deflect the shot back at the same target. This deflection cannot be dodged. The shot deals the attacker's damage.
Rafal Tillo is being shot at by a Stormtrooper. He uses his Deflect Bolts ability and rolls a 10. His WIS is 16. Since the roll succeeds by 6, he manages to deflect the bolt back to the Stormtrooper, who takes his own damage.