If some is distracted, their attention is already focused on something else. If someone is distractible, it is easy for them to become distracted. I was distracted from my work by the noisy party occurring next door. My son is very distractible, so it takes him a long time to finish his homework unless it's very quiet.

Distracted indicates what has already happened. Distractible refers to a tendency that a person has for allowing their mental focus to shift in an undisciplined way.