Well, FWIW, @AgentPete
is allergic to prologues and will embark upon lengthy critical safari if you try and sneak one past him
That being said, I really like them, but as long as they serve a purpose. If something just must be told to the reader that lies outside of the remit/timeline/scope of the main story, I think they can be a fun tease, offering maybe a little foreboding for what is to come. And I do like a good bode.
As to conveying your imaginary world to the reader: hard to say without examples, but its something fantasy/sci-fi writers do everyday. You can normalise your world, just plowing straight forward without explanation and let action show the attributes that are supernormal (eg, your characters are all able to fly, but instead of explaining that, like its odd, you just have them do it). You can have an outside perspective: is everything in your world alien? Is there something/one there can view these alien things with more human eyes, so they can be as surprised as the reader?
Failing that, if you must describe something, be painfully brief. The most simple, word-shy of descriptions tend to be the most powerful. Just hint at the main features and let your reader build their own picture. If you describe something in intimate detail, the readers simply will not get it, and will gloss over your painstaking writing.