dreams have spiritual meanings behind them. most of them offer advice to how to fight a specific dark prinicpality for that day, also, sometimes you might dream something that ends up happening, but this percentage is very low, less than 10%
In a very select few instances, dreams were used by God for specific purposes. But dreams are not a supernatural phenomenon, they are a natural phenomenon. There is still some debate in the scientific community about why we dream; but it's not something unique to humans. Other animals dream, my dog will actually howl at times in her dreams, she's never howled while wake. But yes, dreams are a product of the subconscious, their exact purpose however is unclear, a leading hypothesis is that dreams as a kind of filing system for the brain, the brain is sorting all the information we had while awake and dreams result from this subconscious mental activity.
Dreams come from. 3 sources. Spirit, soul and body. Spiritual = God or Satan. Soul = unconscious dreams from pre occupying subconscious thoughts. Body = too much pizza.
According to Acts 2:17 dreams and visions can be used of God.