If you scare someone, it means you've done something to make them afraid. Afraid is an adjective describing a person with fear, and fear is an emotion (noun).

"What is the difference between...?" "Fear" is usually a noun, and in some formal cases, a verb. The person who fears has the feeling. "Scare" is usually a verb, sometimes a noun. The person who scares does not have the feeling, but gives it to someone else. "Afraid" is an adjective, and we often use "I'm afraid that..." when we introduce bad news.