In terms of interpretation, dreams are what you make of them. Freudians dream about their mothers and Jungians dream about mythological creatures. Those who believe dreams are random nonsense have the most boring dreams of them all. too bad for them.
In terms of science, dreams are typically defined as the memory we have of private experiences that occur in REM sleep, and also hypnagogia or sleep onset. In most REM dreams, the frontal cortex is not activated as much as in waking life, leading to less coherent narratives based on logic or the normal flow of time. Instead, due to an activation of the pons and also the limbic systems, dreams operate on emotional logic, which is a way of connecting long term memories with short term happenings. So by dreaming, we make connections between the past and the present, organized by our own sense of emotional coherence.
So it's best not to think of dreams as "messages" to the waking mind but rather spontaneous expressions or "process" that is part of learning and problem solving. We can focus on this ability - called dream incubation - and use our dreams to help us work through specific issues. Lucid dreaming is another way of honing the dreaming cognition by realizing you are dreaming within the dream, and successfully directing your attention to a topic of interest.