We offered up our own answers in an article that went through scene by scene explaining possible scenarios.
Update: We now get official explanations for the trailer which corroborate some of the below.
Our DC Entertainment source just contacted us and offered the following.
• The Fortress has been on Earth much longer then Kal-El has. It was there before he arrived.
• Kal-El's ship is its own entity. Yes, Lois Lane does find it; she is on an endless quest to find this mystery hero (Clark) that pops up everywhere.
• The voiceover of hers in the trailer is the montage from the end of the movie with the final word being "Superman" (It's very similar to how The Dark Knight ended).
• That tentacled monster is not a monster. It is simply the Black Zero Ship's defences attacking Superman who is trying to disarm it from destroying Metropolis and the Earth.
• Have you noticed that when Zod is shouting "I will find him" at Lara he has no beard? Well, that's because he grows it on his journey to Earth. Zod, Faora, Tor-An and Dev-Em, who are in that picture with him, are about to be put into the Phantom Zone.
And here are a few screen shots from the Man of Steel trailer to go along with it: