The uncertainty comes because scientists can't see the Higgs particle directly. They search for it by smashing protons together, which (so the theory goes) produces Higgs particles. The Higgs particles decay into other particles, and the scientists look for signals from those products of decay in the mass of data that the LHC produces. Unfortunately, there are a lot of other particles, besides the Higgs, being produced and decaying, so there is a lot of background noise and it's very difficult for scientists to know what they're seeing.
The results reported today are consistent with what scientists would expect to see if the Higgs boson really exists. In fact, the chance of these results being seen if the Higgs didn't exist is much less than 1%.
As for what it means for science... it confirms the standard model of physics, but there is still plenty that we don't understand.
I just published a hub about this, with links to previous hubs that I've written about the search for the Higgs particle and unsolved problems in physics: