When "protected" is an adjective, it describes the thing under protection: "A national park is protected land" means that the government protects the park land. This meaning of "protected" usually refers to legal protection.
"Protective" is an adjective that describes the one doing the protecting: "I have protective parents" means that my parents try hard to protect me. "This photo has a protective frame" means that the frame protects the photo.
I hope that helps!