What are dreams and why?

REM sleep is one of the deepest parts of sleep. This is when people dream most frequently. Your body is at it's deepest rest, and the brain has a chance to "catch up" on all the things you took in that day. Your subconscious is doing most of the work, although studies have shown that many parts of the brain are active during sleep. Obviously not ALL of the brain is active, as then you wouldn't be asleep. Essentially, dreams are the result of your brain/mind attempting to sort through at clify all of the information that you've taken in throughout the day. This is also why when you watch a horror movie right before going to sleep, you are more likely to have a nightmare. There is not much known about dreams and what they really mean, but it is most likely that the brain is simply attempting to make heads or tails of all the information that you took in that day. Dreams may also point to issues the brain is having with itself. In other words, if you are depressed, you may have dreams of being an important person or being happy to compensate for your real feelings. All in all, it's a very complex question that psychologists have yet to fully understand. Hopefully I was somewhat helpful.