I keep noticing a lot of news sources going full "Another earth found!"
That's the nasa press release. There's a few key points:
It's in the habitable zone of a star similar to ours and liquid water could exist on the surface. Keplar-22b is one of a few candidates for a series of Earth-like planets, but there is more work to be done to determine whether or not they're actually planets and their specific properties. It's just over double the size of Earth, but they don't know what the surface is like. Its sun is a little smaller and cooler.
So basically, they're looking for Earth-like planets. Kepler 22b could be one due to it's proximity to the star it orbits, the type of star it orbits, and the time it takes to make one full pass around the star. But there's more work to be done and it is by no means a definitive answer.
"Astronomy offers an aesthetic indulgence not duplicated in any other field. This is not an academic or hypothetical attraction and should require no apologies, for the beauty to be found in the skies has been universally appreciated for unrecorded centuries."