TO UNDERSTAND THE MEANING of dreams it helps to have a grasp of mythology and folklore because many symbols are surprisingly persistent and universal. Modern dreams are full of modern things but with a bit of scratching one finds that they are not so different after all to the things that filled our ancestors' dreams. Take keys for example. Your great grandmother will most likely have dreamed of a great big keys out of a fairytale while you might dream of a swipe card, but they mean the same.
Keys are a universal symbol representing the moving from one condition to another, with the key being the choice or action or idea needed to bring about the transition. Keys can also represent power, especially if you dream of a bunch of them, because the person who holds a bunch of keys is in charge of other people's choices. Keys can also represent the keeping of secrets, which can be either good or bad depending on the circumstances.
Dream Dictionaries can be helpful for unravelling common images like this. The sun, moon and stars; kings, queens and princesses - these and many more symbols mean pretty much the same to people everywhere and a good dream dictionary can set you on the path to understanding the dreams in which they appear. Fantasy and mythology are also helpful because they employ the vocabulary of dreams to spin their tales. You just have to remember that dreams often disguise ancient symbols in modern dress.