Hear from sb = If you hear from someone, you get a letter or telephone call from them, or they tell you something
"We haven't heard from her for ages."
"You'll be hearing from my solicitors" (= They will write to you about my complaint).
Hear of sb/sth = If you have heard of someone or something, you know that that person or thing exists
"I'd never heard of him before he won the prize."
"It's a tiny country that most people have never heard of."
Hear about sb/sth = to learn about someone or something. (Not necessarily by hearing.)
"Have you heard about Tom and what happened to him?"
"I heard about the accident."