How do you think about it now? If you have ever had dream in almost your life, then you will think it in different ways. having a dream is not as simple as the way to express it. You can remember it after you wake up, but it’s nothing to do. The important thing is that your dream can aim to something in the past, present or your future. Or just something you have read for long time ago.
Sigmund Freud think that Dream is an explanation what related to your sexual expectation. But Recently, I have read a book of Carl Jung, and he think the different way from Sigmund Freud although Freud inspired for Jung in this type of research.
If you want to know the real answer, read their books and find your own answer.