That sucks.
SPOILER?
Basically it has to do with the Spartans building that wall of dead Persians and then knocking it over on them like we saw in the trailer. There's a bunch of fighting and stabbing. Then the Persians loose that troll-like dude from the trailer, and he starts breaking **** and the clip ends with him fighting Leonidas (Gerard Butler's character).
The video and audio quality are garbage anyway.