While no footage has made its way online as of yet, IGN provided a description from NBC Universal's upfronts.
The Krypton teaser begins in space with a voice over asking, "What remains when a civilization dies?" It's then revealed the footage is shown flying through the destruction of Krypton with green rocks flying by as well. The voice over then states, "This is not the story of how our world died. This is the story of how we lived." Scenes are then showed on Krypton, which resembled those from the beginning of Man of Steel.
Krypton is set two generations before the destruction of the legendary Man of Steel’s home planet. Krypton will follow Superman’s grandfather — whose House of El was ostracized and shamed — as he fights to redeem his family’s honor and save his beloved world from chaos.
Note: I'm not totally sure if this is set in the world of the DC movies or just inspired by it, though a while back Goyer did state it was and is set 200 years prior to the events from Man of Steel. If the latter is the case, then Krypton would be the first DC TV series to connect to the movies.