Apple seeds do contain a cyanide compound. But they don't contain much cyanide, and the seeds' shell prevents the poison from entering the body. So there's not much danger.
Apple seeds have a small amount of cyanide poisoning in them. It's extremely unlikely that a person, even an avid apple-eater, will eat enough seeds to have any adverse effects.
For the human diet, apple seeds cannot be digested, acting as dietary fiber. Some seeds have tanins that can make people sick but you would have to eat a lot!
