What determines how a person dreams?

The question cannot be answered meaningfully as it is phrased. All humans dream in the same way, so "how" a person dreams is determined by being human. The mind, which is a function of the brain, produces dreams during sleep. Not everyone remembers their dreams, and various factors can influence the experience of dreaming. Those factors include illness, such as fever, which causes vivid, disturbing dreams, as well as alcohol, caffeine, various medications and drugs, and physical discomfort experienced during sleep. See the link below for further information and additional resources.