If i relax , i hear voices crying and talking to me. if i pay attention for exemple studying , this doesn't happend.are these hallucinations?

Possibly, or not: Hallucinations are sensory experiences without external stimuli. Illusions are sensory experiences that come with external stimuli that are misinterpreted by the brain. I can't say which you're having from your question alone. Sometimes people who are grieving hear voices like this. Please see a psychiatrist in your community to further explore what's happening with you, and get help. Be well.