When dreaming, we are usually located on mental plane level, more seldom on astral plane, even more seldom on ethereal one, and in exceptional cases on casual and intuitive planes level.
Mental and astral planes penetrate the space through. Mental plane is a universal reality which consists of mental energy, ideas and thoughts. Astral plan contains all our emotions, reaction, desires and passions, including sordid ones. That is why there is a division into high and low levels of astral plane, as lower are a real storage of filth.
Everything that happens in our dreams is a projection of our thoughts in the inner world restored by images and plots from our memory storage, including unconscious one. Any action in a dream is a thought of the dreamer him(her)self. If to express our desires in physical world we are first of all to use our material body sending impulses from the brain to nerve terminals, in a dream we just need to think of something or somebody.