What information on dreams would be helpful?

after learning about the oneiroi of greek mythology and a grown interest in plots of dreams I'm thinking about writing a novel centered on people who dream lucidly or enter others' dreams and retrieve objects and characters from those dreams or manipulate their events toward some end. I'm having trouble thinking of a plot to go with the setting, though, and finding well-explained info or theories on what dreams are, why we have them, how they affect us and we affect them, etc, All I really have is the setting and a main character who's been disillusioned from seeing into others' subconscious (by dreams). I could really use some help with learning about the relation of these subconsciouses to the dreams from them, a conflict that could face this character/(an) antagonist(s), and I'm also looking to learn more about Jung's collective unconscious and its effect on multiple dreams.